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                                                                    EXHIBIT 4.5


                          FOURTH SUPPLEMENTAL INDENTURE


     FOURTH SUPPLEMENTAL INDENTURE, dated as of January 31, 2002 (this "Fourth
Supplemental Indenture"), between NorthWestern Corporation, a Delaware
corporation (the "Company"), and JPMorgan Chase Bank (as successor to The Chase
Manhattan Bank), as trustee (the "Trustee") under the Indenture dated as of
August 1, 1995 between the Company and the Trustee (such Indenture, as
previously supplemented and as further supplemented by this Fourth Supplemental
Indenture, the "Indenture").

     WHEREAS, the Company executed and delivered the Indenture to the Trustee to
provide for the future issuance of the Company's subordinated debt securities,
to be issued from time to time in one or more series as might be determined by
the Company under the Indenture, in an unlimited aggregate principal amount
which may be authenticated and delivered as provided in the Indenture;

     WHEREAS, pursuant to the terms of the Indenture, the Company desires to
provide for the establishment of a new series of its Securities to be known as
its 8.10% Junior Subordinated Deferrable Interest Debentures due January 15,
2032 (the "Subordinated Debentures"), the form and substance of such
Subordinated Debentures and the terms, provisions and conditions thereof to be
set forth as provided in the Indenture and this Fourth Supplemental Indenture;

     WHEREAS, NorthWestern Capital Financing III, a Delaware statutory business
trust (the "Trust"), has offered to the public $100,000,000 aggregate
liquidation amount of its 8.10% Trust Preferred Securities (the "Preferred
Securities") and has offered to the Company $3,092,800 in aggregate liquidation
amount of its 8.10% Trust Common Securities (the "Common Securities"), each
representing undivided beneficial interests in the assets of the Trust, and
proposes to invest the proceeds from such offerings in $103,092,800 aggregate
principal amount of the Subordinated Debentures; and

     WHEREAS, the Trust has entered into an overallotment option (the
"Overallotment Option") in the Underwriting Agreement (the "Underwriting
Agreement"), dated as of January 24, 2002, among the Company, the Trust and
Morgan Stanley & Co. Incorporated, Merrill Lynch & Co., Merrill Lynch, Pierce,
Fenner & Smith Incorporated and Salomon Smith Barney Inc., as representatives of
the several Underwriters named in Schedule A thereto, pursuant to which the
Preferred Securities are sold whereby the Trust, within 30 days after the
issuance of the Preferred Securities, may issue up to an additional $15,000,000
in aggregate liquidation amount of the Preferred Securities and an additional
$463,925 in aggregate liquidation amount of the Common Securities and proposes
to invest the proceeds from the Overallotment Option in an equivalent aggregate
principal amount of Subordinated Debentures; and

     WHEREAS, the Company has requested that the Trustee execute and deliver
this Fourth Supplemental Indenture, and all requirements necessary to make this
Fourth Supplemental Indenture a valid instrument in accordance with its terms
(and to make the Subordinated Debentures, when executed by the Company and
authenticated and delivered by the Trustee, the valid obligations of the
Company) have been performed, and the execution and delivery of this Fourth
Supplemental Indenture has been duly authorized in all respects.

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     NOW THEREFORE, in consideration of the purchase and acceptance of the
Subordinated Debentures by the Holders thereof, and for the purpose of setting
forth, as provided in the Indenture, the form and substance of the Subordinated
Debentures and the terms, provisions and conditions thereof, the Company
covenants and agrees with the Trustee as follows:

                                    ARTICLE I
                                   DEFINITIONS

     SECTION 1.1. Definition of Terms.

     Unless the context otherwise requires:

     (a)  a term not defined herein that is defined in the Indenture has the
          same meaning when used in this Fourth Supplemental Indenture;

     (b)  a term defined anywhere in this Fourth Supplemental Indenture has the
          same meaning throughout;

     (c)  the singular includes the plural and vice versa;

     (d)  a reference to a Section or Article is to a Section or Article of this
          Fourth Supplemental Indenture;

     (e)  headings are for convenience of reference only and do not affect
          interpretation;

     (f)  the Trust shall be deemed to be an "NWPS Trust" for purposes of the
          Indenture;

     (g)  the following terms have the meanings given to them in the
          Declaration: (i) Business Day; (ii) Clearing Agency; (iii) Delaware
          Trustee; (iv) Distribution; (v) Property Trustee; (vi) Preferred
          Securities Guarantee; (vii) Preferred Security Certificate; and (viii)
          Regular Trustees; and

     (h)  the following terms have the meanings given to them in this Section
          1.1(h):

               "Additional Sums" has the meaning specified in Section 2.5(c).

               "Compounded Interest" has the meaning specified in Section 4.1.

               "Declaration" means the Amended and Restated Declaration of Trust
          of the Trust, dated as of January 31, 2002, as amended or restated
          from time to time.

               "Direct Action" has the meaning specified in Section 10.2.

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               "Dissolution Event" means that, as a result of the occurrence and
          continuation of a Tax Event or an Investment Company Event or at the
          option of the Company, the Trust is to be dissolved in accordance with
          the Declaration, and the Subordinated Debentures held by the Property
          Trustee are to be distributed to the holders of the Trust Securities
          issued by the Trust pro rata in accordance with the Declaration.

               "Investment Company Event" means the receipt by the Trust of an
          opinion of counsel to the Company experienced in such matters to the
          effect that, as a result of the occurrence of an amendment to or a
          change in law or regulation or a written change (including any
          announced prospective change) in law or regulation or a change in
          interpretation or application of law or regulation by any legislative
          body, court, governmental agency or regulatory authority, there is
          more than an insubstantial risk that the Trust is or will be
          considered an "investment company" that is required to be registered
          under the Investment Company Act, which change or prospective change
          becomes effective or would become effective, as the case may be, on or
          after the date of the issuance of the Subordinated Debentures.

               "Maturity Date" has the meaning specified in Section 2.2.

               "Senior Indebtedness" means (i) the principal, premium, if any,
          and interest in respect of (A) indebtedness of the Company for money
          borrowed and (B) indebtedness evidenced by securities, debentures,
          bonds or other similar instruments issued by the Company, including,
          without limitation, all obligations under its General Mortgage and
          Deed of Trust dated as of August 1, 1993 between the Company and
          JPMorgan Chase Bank, as successor to The Chase Manhattan Bank, as
          trustee, and the Indenture dated as of November 1, 1998 between the
          Company and JPMorgan Chase Bank, as trustee; (ii) all capital lease
          obligations of the Company; (iii) all obligations of the Company
          issued or assumed as the deferred purchase price of property, all
          conditional sale obligations of the Company and all obligations of the
          Company under any title retention agreement (but excluding trade
          accounts payable arising in the ordinary course of business); (iv) all
          obligations of the Company for the reimbursement on any letter of
          credit, banker's acceptance, security purchase facility or similar
          credit transaction; (v) all obligations of the type referred to in
          clauses (i) through (iv) of other Persons for the payment of which the
          Company is responsible or liable as obligor, guarantor or otherwise;
          and (vi) all obligations of the type referred to in clauses (i)
          through (v) of other Persons secured by any lien on any property or
          asset of the Company (whether or not such obligation is assumed by the
          Company), except for (a) any such indebtedness that is by its terms
          subordinated to or pari passu with the Subordinated Debentures and (b)
          any indebtedness between or among the Company and its Affiliates,
          including all other debt securities and guarantees in respect of those
          debt securities, issued to any other trust, or a trustee of such
          trust, partnership or other entity affiliated with the Company which
          is a financing vehicle of the Company ("Financing Entity") in
          connection with the issuance by such Financing Entity of preferred
          securities or other securities that rank pari passu with, or junior
          to, the Preferred Securities.

               "Tax Event" means the receipt by the Trust of an opinion of
          counsel to the Company experienced in such matters to the effect that,
          as a result of any amendment to, or change (including any announced
          prospective change) in, the laws (or any regulations thereunder) of
          the United States or any political subdivision or taxing authority
          thereof or therein, or as a result of any official or administrative
          pronouncement or action or judicial decision interpreting or

<PAGE>

          applying such laws or regulations, which amendment or change is
          effective or which pronouncement, action or decision is announced or
          occurs on or after the date of issuance of the Subordinated
          Debentures, there is more than an insubstantial risk that (i) the
          Trust is or will be within 90 days of the delivery of such opinion,
          subject to United States federal income tax with respect to interest
          received or accrued on the Subordinated Debentures, (ii) interest
          payable by the Company on the Subordinated Debentures is not, or
          within 90 days of the delivery of such opinion will not be, deductible
          by the Company, in whole or in part, for United States federal income
          tax purposes, or (iii) the Trust is, or will be within 90 days of the
          delivery of such opinion, subject to more than a minimal amount of
          other taxes, duties, assessments or other governmental charges.

                                   ARTICLE II
                 GENERAL TERMS AND CONDITIONS OF THE DEBENTURES

     SECTION 2.1. Designation and Principal Amount.

     There is hereby authorized a series of Securities designated the "8.10%
Junior Subordinated Deferrable Interest Debentures due January 15, 2032,"
limited in aggregate principal amount to $103,092,800, PROVIDED, HOWEVER, that
if the Overallotment Option is exercised, the aggregate principal amount of the
Subordinated Debentures may be increased to up to an aggregate principal amount
of $118,556,725 which amount shall be as set forth in any written Company Order
for the authentication and delivery of Subordinated Debentures pursuant to
Section 303 of the Indenture.

     SECTION 2.2. Maturity.

     The Scheduled Maturity Date will be January 15, 2032.

     SECTION 2.3. Form and Payment.

     Except as provided in Section 2.4, the Subordinated Debentures shall be
issued as Registered Securities in fully registered certificated form without
interest coupons. Principal of and interest on the Subordinated Debentures
issued in certificated form will be payable, the transfer of such Subordinated
Debentures will be registrable and such Subordinated Debentures will be
exchangeable for Subordinated Debentures bearing identical terms and provisions
at the office or agency of the Trustee; PROVIDED, HOWEVER, that payment of
interest may be made at the option of the Company by check mailed to the Holder
at such address as shall appear in the Security Register. Notwithstanding the
foregoing, so long as the Holder of any Subordinated Debentures is the Property
Trustee, the payment of the principal of and interest (including Compounded
Interest and Additional Sums, if any) on such Subordinated Debentures held by
the Property Trustee will be made at such place and to such account as may be
designated by the Property Trustee.

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     SECTION 2.4. Global Debenture.

     (a) In connection with a Dissolution Event:

          (i)  The Subordinated Debentures in certificated form may be presented
               to the Trustee by the Property Trustee in exchange for a global
               Subordinated Debenture in an aggregate principal amount equal to
               all Outstanding Subordinated Debentures (a "Global Debenture"),
               to be registered in the name of The Depository Trust Company (the
               "Depository"), or its nominee, and delivered by the Trustee to
               the Depository or a custodian appointed by the Depository for
               crediting to the accounts of its participants pursuant to the
               instructions of the Regular Trustees. The Company upon any such
               presentation shall execute a Global Debenture in such aggregate
               principal amount and deliver the same to the Trustee for
               authentication and delivery in accordance with the Indenture and
               this Fourth Supplemental Indenture. Payments on the Subordinated
               Debentures issued as a Global Debenture will be made to the
               Depository.

          (ii) If any Preferred Securities are held in non book-entry
               certificated form, the Subordinated Debentures in certificated
               form may be presented to the Trustee by the Property Trustee, and
               any Preferred Security Certificate which represents Preferred
               Securities other than Preferred Securities held by the Depository
               or its nominee ("Non Book-Entry Preferred Securities") will be
               deemed to represent beneficial interests in Subordinated
               Debentures presented to the Trustee by the Property Trustee
               having an aggregate principal amount equal to the aggregate
               liquidation amount of the Non Book-Entry Preferred Securities
               until such Preferred Security Certificates are presented to the
               Security Registrar for transfer or reissuance, at which time such
               Preferred Security Certificates will be canceled and a
               Subordinated Debenture registered in the name of the holder of
               the Preferred Security Certificate or the transferee of the
               holder of such Preferred Security Certificate, as the case may
               be, with an aggregate principal amount equal to the aggregate
               liquidation amount of the Preferred Security Certificate canceled
               will be executed by the Company and delivered to the Trustee for
               authentication and delivery in accordance with the Indenture and
               this Fourth Supplemental Indenture. On issue of such Subordinated
               Debentures, Subordinated Debentures with an equivalent aggregate
               principal amount that were presented by the Property Trustee to
               the Trustee will be deemed to have been canceled.

     (b) A Global Debenture may be transferred, in whole but not in part, only
by the Depository to a nominee of the Depository, by a nominee of the Depository
to

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another nominee of the Depository, or by the Depository or such nominee to a
successor Depository selected or approved by the Company or to a nominee of such
successor Depository.

     (c) If at any time the Depository notifies the Company that it is unwilling
or unable to continue as Depository for the Subordinated Debentures or if at any
time the Depository ceases to be a clearing agency registered under the
Securities Exchange Act of 1934, as amended, or other applicable statute or
regulation, at a time the Depository is required to be so registered, and a
successor Depository is not appointed by the Company within 90 days after the
Company receives such notice or becomes aware of such condition, as the case may
be, the Company will execute, and, subject to Article Two of the Indenture, the
Trustee will authenticate and deliver, the Subordinated Debentures in definitive
registered form without coupons, in authorized denominations, and in an
aggregate principal amount equal to the principal amount of the Global Debenture
in exchange for such Global Debenture. In addition, if at any time the Company
determines that the Subordinated Debentures shall no longer be represented by a
Global Debenture or there shall have occurred an Event of Default, the Company
will execute, and, subject to receipt of a certificate evidencing such
determination by the Company, the Trustee will authenticate and deliver, the
Subordinated Debentures in definitive registered form without coupons, in
authorized denominations, and in an aggregate principal amount equal to the
principal amount of the Global Debenture in exchange for such Global Debenture.
Upon the exchange of the Global Debenture for such Subordinated Debentures in
definitive registered form without coupons, in authorized denominations, the
Global Debenture shall be canceled by the Trustee. Such Subordinated Debentures
in definitive registered form issued in exchange for the Global Debenture shall
be registered in such names and in such authorized denominations as the
Depository, pursuant to instructions from its direct or indirect participants or
otherwise, shall instruct the Trustee. The Trustee shall deliver such Securities
to the Depository for delivery to the Persons in whose names such Securities are
so registered.

     SECTION 2.5. Interest.

     (a) Each Subordinated Debenture will bear interest at the rate of 8.10% per
annum (the "Coupon Rate") from its original date of issuance or from the most
recent Interest Payment Date (as defined below) to which interest has been paid
or duly provided for until the principal thereof becomes due and payable, and on
any overdue principal and (to the extent that payment of such interest is
enforceable under applicable law) on any overdue installment of interest at the
Coupon Rate, compounded quarterly, payable (subject to the provisions of Article
Four) quarterly in arrears on January 15, April 15, July 15 and October 15 of
each year (each, an "Interest Payment Date"), commencing on April 15, 2002 to
the Person in whose name such Subordinated Debenture or any Predecessor Security
is registered, at the close of business on the Regular Record Date for such
interest installment, which, in respect of any Subordinated Debentures of which
the Property Trustee is the Holder or a Global Debenture, shall be the close of
business on the Business Day next preceding that Interest Payment Date;
PROVIDED, HOWEVER, that interest paid at maturity shall be paid to the Person to
whom principal is paid. Notwithstanding the foregoing sentence, if the Preferred
Securities are no longer in book-entry only form or if pursuant to the Indenture
the Subordinated Debentures are not represented by a Global Debenture, the
Regular Record Date for such interest installment shall be 15 Business Days
before the relevant Interest Payment Date. Any interest on any Subordinated

<PAGE>


Debenture which is payable but is not punctually paid or duly provided for on
any Interest Payment Date shall forthwith cease to be payable to the Holder on
the relevant Regular Record Date by virtue of having been such Holder, and such
defaulted interest and interest on such defaulted interest (to the extent
lawful) at the Coupon Rate may be paid by the Company, at its election, (i) to
the Persons in whose names the Subordinated Debentures (or their respective
Predecessor Securities) are registered at the close of business on a Special
Record Date to be fixed by the Company for such payment, notice of which shall
be not more than 15 days and not less than 10 days prior to the date of the
proposed payment, or (ii) in any other lawful manner not inconsistent with the
requirements of any securities exchange on which the Subordinated Debentures may
be listed, and upon such notice as may be required by such exchange, all as more
fully provided in Section 307 of the Indenture.

     (b) The amount of interest payable for any period will be computed on the
basis of a 360-day year of twelve 30-day months. Except as provided in the
following sentence, the amount of interest payable for any period shorter than a
full quarterly period for which interest in computed will be computed on the
basis of the actual number of days elapsed in such a 30-day month. In the event
that any date on which interest is payable on the Subordinated Debentures is not
a Business Day, then payment of interest payable on such date will be made on
the next succeeding day which is a Business Day (and without any interest or
other payment in respect of any such delay), except that, if such Business Day
is in the next succeeding calendar year, such payment shall be made on the
immediately preceding Business Day, in each case with the same force and effect
as if made on such date.

     (c) If, at any time while the Property Trustee is the Holder of any
Subordinated Debentures, the Trust or the Property Trustee is required to pay
any taxes, duties, assessments or governmental charges of whatever nature (other
than withholding taxes) imposed by the United States or any other taxing
authority (including, without limitation, if an event described in clause (i) or
(iii) of the definition of Tax Event has occurred and is continuing), then, in
any case, the Company will pay as additional interest ("Additional Sums") on the
Subordinated Debentures held by the Property Trustee such additional amounts as
shall be required so that the net amounts received and retained by the Trust and
the Property Trustee after paying such taxes, duties, assessments or other
governmental charges will be equal to the amounts the Trust and the Property
Trustee would have received had no such taxes, duties, assessments or other
government charges been imposed.

                                  ARTICLE III
                          REDEMPTION OF THE DEBENTURES

     SECTION 3.1. Special Event Redemption.

     If, prior to January 31, 2007, a Tax Event or an Investment Company Event
has occurred and is continuing then, notwithstanding Section 3.2, the Company
shall have the right upon not less than 30 nor more than 60 days' notice to the
Holders of the Subordinated Debentures to redeem the Subordinated Debentures in
whole (but not in part) within 90 days following the occurrence of such Tax
Event or Investment Company Event at a redemption price equal to 100% of the
principal amount to be redeemed plus any accrued and unpaid interest thereon
(including Compounded Interest and Additional Sums, if any) to the date of such
redemption

<PAGE>

(the "Redemption Price"). The Redemption Price shall be paid prior to 12:00
noon, New York time, on the date of such redemption or such earlier time as the
Company determines, provided that the Company shall have deposited with the
Trustee an amount sufficient to pay the Redemption Price by 10:00 a.m. on the
date such Redemption Price is to be paid. Such redemption shall otherwise be in
accordance with the provisions of Article Eleven of the Indenture.

     SECTION 3.2. Optional Redemption by Company.

     (a) Subject to the provisions of Section 3.2(b) and to the provisions of
Article Eleven of the Indenture, except as otherwise may be specified in this
Fourth Supplemental Indenture, the Company shall have the right to redeem the
Subordinated Debentures, in whole or in part, from time to time, on or after
January 31, 2007 at the Redemption Price. Any redemption pursuant to this
paragraph will be made upon not less than 30 nor more than 60 days' notice to
the Holder of the Subordinated Debentures. If the Subordinated Debentures are
only partially redeemed pursuant to this Section 3.2, the particular
Subordinated Debentures to be redeemed will be selected on a pro rata basis by
such method as the Trustee shall deem fair and appropriate or, if at the time of
redemption the Subordinated Debentures are registered as a Global Debenture, in
accordance with the Depository's customary procedures. The Redemption Price
shall be paid prior to 12:00 noon, New York time, on the date of such redemption
or at such earlier time as the Company determines, provided that the Company
shall have deposited with the Trustee an amount sufficient to pay the Redemption
Price by 10:00 a.m. on the date such Redemption Price is to be paid.

     (b) The Company may not redeem fewer than all of the Subordinated
Debentures unless all accrued and unpaid interest has been paid on all
Subordinated Debentures for all quarterly interest payment periods terminating
on or prior to the date of redemption. If a partial redemption of the
Subordinated Debentures would result in the delisting of the Preferred
Securities issued by the Trust from any national securities exchange or other
organization on which the Preferred Securities are then listed, the Company
shall not be permitted to effect such partial redemption and may only redeem the
Subordinated Debentures in whole.

     SECTION 3.3. No Sinking Fund.

     The Subordinated Debentures are not entitled to the benefit of any sinking
fund.

                                   ARTICLE IV
                      EXTENSION OF INTEREST PAYMENT PERIOD

     SECTION 4.1. Extension of Interest Payment Period.

     So long as no Event of Default has occurred and is continuing, the Company
shall have the right, at any time during the term of the Subordinated
Debentures, from time to time to defer payments of interest by extending the
interest payment period of such Subordinated Debentures for up to 20 consecutive
quarters, but not beyond the Maturity Date of the Subordinated Debentures (the
"Extended Interest Payment Period"). To the extent permitted by applicable law,
interest, the payment of which has been deferred because of the extension of the
interest payment

<PAGE>

period pursuant to this Section 4.1, will bear interest thereon at the Coupon
Rate compounded quarterly for each quarter of the Extended Interest Payment
Period ("Compounded Interest"). At the end of the Extended Interest Payment
Period the Company shall pay all interest accrued and unpaid on the Subordinated
Debentures, including any Additional Sums and Compounded Interest ("Deferred
Interest") that shall be payable, to the Holders of the Subordinated Debentures
in whose names the Subordinated Debentures are registered in the Security
Register on the first Regular Record Date after the end of the Extended Interest
Payment Period. Before the termination of any Extended Interest Payment Period,
the Company may further extend such period, provided that such period together
with all such previous and further extensions thereof shall not exceed 20
consecutive quarters or extend beyond the Maturity Date. Upon the termination of
any Extended Interest Payment Period and upon the payment of all Deferred
Interest then due, the Company may commence a new Extended Interest Payment
Period, subject to the foregoing requirements. No interest shall be due and
payable during an Extended Interest Payment Period, except at the end thereof.

     SECTION 4.2. Notice of Extension.

     (a) If the Property Trustee is the only registered Holder of the
Subordinated Debentures at the time the Company selects an Extended Interest
Payment Period, the Company shall give written notice to the Regular Trustees,
the Property Trustee and the Trustee of its selection of such Extended Interest
Payment Period one Business Day before the earlier of (i) the next succeeding
date on which Distributions on the Trust Securities issued by the Trust are
payable, or (ii) the date the Trust is required to give notice of the record
date or the date such Distributions are payable to the New York Stock Exchange
or other applicable self-regulatory organization or to holders of the Preferred
Securities issued by the Trust, but in any event at least one Business Day
before such record date.

     (b) If the Property Trustee is not the only Holder of the Subordinated
Debentures at the time the Company selects an Extended Interest Payment Period,
the Company shall give the Holders of the Subordinated Debentures and the
Trustee written notice of its selection of such Extended Interest Payment Period
10 Business Days before the earlier of (i) the next succeeding Interest Payment
Date, or (ii) the date the Company is required to give notice of the record or
payment date of such interest payment to the New York Stock Exchange or other
applicable self-regulatory organization or to Holders of the Subordinated
Debentures.

     (c) The quarter in which any notice is given pursuant to paragraphs (a) or
(b) of this Section 4.2 shall be counted as one of the 20 quarters permitted in
the maximum Extended Interest Payment Period permitted under Section 4.1.

     SECTION 4.3. Restrictions on Payments.

     So long as any Subordinated Debentures remain outstanding, if there shall
have occurred an Event of Default (as defined in the Indenture), or an event of
which the Company has actual knowledge that, with the giving of notice or the
lapse of time or both, would constitute an Event of Default under the Indenture
and in respect of which the Company shall not have taken reasonable steps to
cure or the Company is in default with respect to the payment of any obligations
under the Preferred Securities Guarantee, or if the Company has given notice of
its

<PAGE>

selection of an Extended Interest Payment Period with respect to the
Subordinated Debentures pursuant to Section 4.1 hereof and shall not have
rescinded such notice, or such Excluded Interest Payment Period, or any
extension thereof, is continuing, then, in each case, (a) the Company shall not
declare or pay any dividend on, or make any distribution with respect to, or
redeem, purchase, acquire or make a liquidation payment with respect to, any of
its capital stock, (b) the Company shall not make any payment of interest,
principal or premium, if any, on or repay, repurchase or redeem any debt
securities (including guarantees of indebtedness for money borrowed) issued by
the Company which rank pari passu with or junior to the Subordinated Debentures,
and (c) the Company shall not make any payments with respect to any guarantee of
a debt security of any of the Company's subsidiaries (including other
guarantees) if such guarantee ranks pari passu with or junior to the
Subordinated Debentures; provided that the foregoing restrictions in this
Section 4.3 shall not apply to (i) repurchases, redemptions or other
acquisitions of shares of capital stock of the Company (A) in connection with
any employment contract, benefit plan or other similar arrangement with or for
the benefit of any one or more employees, officers, directors or consultants or
(B) in connection with a dividend reinvestment or stockholder stock purchase
plan, (ii) the issuance of common stock of the Company (or securities
convertible into or exercisable for such common stock) as consideration in an
acquisition transaction entered into prior to such Extended Interest Payment
Period, (iii) the reclassification of the capital stock of the Company or the
exchange or conversion of any class or series of the Company's capital stock for
another class or series of the Company's capital stock, provided that such
reclassification, exchange or conversion does not include any cash payments,
(iv) the purchase of fractional interests in shares of the Company's capital
stock pursuant to the conversion or exchange provisions of such capital stock or
the security being converted or exchanged, (v) the issuance of the capital stock
of the Company in connection with the exercise of certain rights on convertible
securities, (vi) any dividend in the form of common stock, warrants, options or
other rights where the dividend stock or the stock issuable upon exercise of
such warrants, options or other rights is common stock, or (vii) payments by the
Company under the Preferred Securities Guarantee or under any similar guarantee
by the Company with respect to any securities of its subsidiaries that are made
on a pro rata basis on all such guarantees, provided the proceeds from the
issuance of such securities were used to purchase Subordinated Debentures.

                                   ARTICLE V
                                    EXPENSES

     SECTION 5.1. Payment of Expenses.

     In connection with the offering, sale and issuance of the Subordinated
Debentures to the Property Trustee in connection with the sale of the Trust
Securities by the Trust, the Company shall:

     (a) pay for all costs and expenses relating to the offering, sale and
issuance of the Subordinated Debentures, including commissions to the
underwriters payable pursuant to the Underwriting Agreement and compensation of
the Trustee under the Indenture in accordance with the provisions of Section 607
of the Indenture; and

<PAGE>

     (b) pay for all costs and expenses of the Trust, including, but not limited
to, costs and expenses relating to the organization of the Trust, the offering,
sale and issuance of the Trust Securities (including commissions to the
underwriters payable pursuant to the Underwriting Agreement in connection
therewith); the fees and expenses of the Property Trustee (including, without
limitation, those incurred in connection with the enforcement by the Property
Trustee of the rights of the holders of the Preferred Securities), the Delaware
Trustee and the Regular Trustees; the costs and expenses relating to the
operation of the Trust (including, without limitation, costs and expenses of
accountants, attorneys, statistical or bookkeeping services, expenses for
printing and engraving and computing or accounting equipment, paying agent(s),
registrar(s), transfer agent(s), duplicating, travel and telephone and other
telecommunications expenses); and costs and expenses incurred in connection with
the acquisition, financing and disposition of Trust assets; and

     (c) pay any and all taxes (other than United States withholding taxes
attributable to the Trust or its assets) and all liabilities, costs and expenses
with respect to such taxes of the Trust.

                                   ARTICLE VI
                                  SUBORDINATION

     SECTION 6.1. Agreement to Subordinate.

     The Company covenants and agrees, and each Holder of Subordinated
Debentures issued hereunder by such Holder's acceptance thereof likewise
covenants and agrees, that all Subordinated Debentures shall be issued subject
to the provisions of this Article Six; and each Holder of a Subordinated
Debenture, whether upon original issue or upon transfer or assignment thereof,
accepts and agrees to be bound by such provisions. The payment by the Company of
the principal of and premium, if any, and interest on all Subordinated
Debentures issued hereunder shall, to the extent and in the manner hereinafter
set forth, be subordinated and junior in right of payment to the prior payment
in full of all Senior Indebtedness, whether outstanding at the date of this
Supplemental Indenture or hereafter incurred. No provision of this Article Six
shall prevent the occurrence of any default or Event of Default.

     SECTION 6.2. Default on Senior Indebtedness.

     In the event and during the continuation of any default by the Company in
the payment of principal, premium, interest or any other payment due on any
Senior Indebtedness, or in the event that any applicable grace period with
respect to such default has ended and such default has not been cured or waived
or ceased to exist, or in the event that the maturity of any Senior Indebtedness
has been accelerated because of a default, then, in either case, no payment
shall be made by the Company with respect to the principal (including redemption
and sinking fund payments) of, or premium, if any, or interest on the
Subordinated Debentures. In the event that, notwithstanding the foregoing, any
payment shall be received by the Trustee when such payment is prohibited by the
preceding paragraph of this Section 6.2, such payment shall be held in trust for
the benefit of, and shall be paid over or delivered to, the holders of such
Senior Indebtedness or their respective representatives, or to the trustee or
trustees under any indenture pursuant to which any Senior Indebtedness may have
been issued, as their respective interests may appear,

<PAGE>

but only to the extent that the holders of such Senior Indebtedness (or their
representative or representatives or a trustee) notify the Trustee in writing
within 90 days of such payment of the amounts then due and owing on such Senior
Indebtedness, and only the amounts specified in such notice to the Trustee shall
be paid to the holders of such Senior Indebtedness.

     SECTION 6.3. Liquidation; Dissolution; Bankruptcy.

     Upon any payment by the Company or distribution of assets of the Company of
any kind or character, whether in cash, property or securities, to creditors
upon any dissolution or winding-up or liquidation or reorganization of the
Company, whether voluntary or involuntary or in bankruptcy, insolvency,
receivership or other proceedings, all amounts due upon all Senior Indebtedness
shall first be paid in full, or payment thereof provided for in money in
accordance with its terms, before any payment is made by the Company on account
of the principal (and premium, if any) or interest on the Subordinated
Debentures; and upon any such dissolution or winding-up or liquidation or
reorganization, any payment by the Company, or distribution of assets of the
Company of any kind or character, whether in cash, property or securities, which
the Holders of the Subordinated Debenture or the Trustee would be entitled to
receive from the Company, except for the provisions of this Article Six, shall
be paid by the Company or by any receiver, trustee in bankruptcy, liquidating
trustee, agent or other Person making such payment or distribution, or by the
Holders of the Subordinated Debentures or by the Trustee under the Indenture if
received by them or it, directly to the holders of any Senior Indebtedness (pro
rata to such holders on the basis of the respective amounts of Senior
Indebtedness held by such holders, as calculated by the Company) or their
representative or representatives, or to the trustee or trustees under any
indenture pursuant to which any instruments evidencing such Senior Indebtedness
may have been issued, as their respective interests may appear, to the extent
necessary to pay such Senior Indebtedness in full, in money or money's worth,
after giving effect to any concurrent payment or distribution to or for the
holders of such Senior Indebtedness, before any payment or distribution is made
to the Holders of Subordinated Debentures or to the Trustee.

     In the event that, notwithstanding the foregoing, any payment or
distribution of assets of the Company of any kind or character, whether in cash,
property or securities, prohibited by the foregoing, shall be received by the
Trustee before all Senior Indebtedness is paid in full, or provision is made for
such payment in money in accordance with its terms, such payment or distribution
shall be held in trust for the benefit of and shall be paid over or delivered to
the holders of such Senior Indebtedness or their representative or
representatives, or to the trustee or trustees under any indenture pursuant to
which any instruments evidencing such Senior Indebtedness may have been issued,
as their respective interests may appear, as calculated by the Company, for
application to the payment of all Senior Indebtedness remaining unpaid to the
extent necessary to pay such Senior Indebtedness in full in money in accordance
with its terms, after giving effect to any concurrent payment or distribution to
or for the holders of such Senior Indebtedness.

     For purposes of this Article Six, the words "cash, property or securities"
shall not be deemed to include shares of stock of the Company as reorganized or
readjusted, or securities of the Company or any other corporation provided for
by a plan of reorganization or readjustment, the payment of which is
subordinated at least to the extent provided in this Article Six with

<PAGE>

respect to the Subordinated Debentures to the payment of all Senior Indebtedness
that may at the time be outstanding, provided that (i) such Senior Indebtedness
is assumed by the new corporation, if any, resulting from any such
reorganization or readjustment, and (ii) the rights of the holders of such
Senior Indebtedness are not, without the consent of such holders, altered by
such reorganization or readjustment. The consolidation of the Company with, or
the merger of the Company into, another corporation or the liquidation or
dissolution of the Company following the conveyance or transfer of its property
as an entirety, or substantially as an entirety, to another corporation upon the
terms and conditions provided for in Article Eight of the Indenture shall not be
deemed a dissolution, winding-up, liquidation or reorganization for the purposes
of this Section 6.3 if such other corporation shall, as a part of such
consolidation, merger, conveyance or transfer, comply with the conditions stated
in Article Eight of the Indenture. Nothing in Section 6.2 or in this Section 6.3
shall apply to claims of, or payments to, the Trustee under or pursuant to
Section 606 of the Indenture.

     SECTION 6.4. Subrogation.

     Subject to the payment in full of all Senior Indebtedness, the rights of
the Holders of the Subordinated Debentures shall be subrogated to the rights of
the holders of such Senior Indebtedness to receive payments or distributions of
cash, property or securities of the Company, as the case may be, applicable to
such Senior Indebtedness until the principal of (and premium, if any) and
interest on the Subordinated Debentures shall be paid in full; and, for the
purposes of such subrogation, no payments or distributions to the holders of
such Senior Indebtedness of any cash, property or securities to which the
Holders of the Subordinated Debentures or the Trustee would be entitled except
for the provisions of this Article Six, and no payment over pursuant to the
provisions of this Article Six to or for the benefit of the holders of such
Senior Indebtedness by Holders of the Subordinated Debentures or the Trustee
shall, as between the Company, its creditors other than holders of Senior
Indebtedness and the Holders of the Subordinated Debentures, be deemed to be a
payment by the Company to or on account of such Senior Indebtedness. It is
understood that the provisions of this Article Six are and are intended solely
for the purposes of defining the relative rights of the Holders of the
Subordinated Debentures, on the one hand, and the holders of such Senior
Indebtedness on the other hand.

     Nothing contained in this Article Six or elsewhere in the Indenture or in
the Subordinated Debentures is intended to or shall impair, as between the
Company, its creditors other than the holders of Senior Indebtedness and the
Holders of the Subordinated Debentures, the obligation of the Company, which is
absolute and unconditional, to pay to the Holders of the Subordinated Debentures
the principal of (and premium, if any) and interest on the Subordinated
Debentures as and when the same shall become due and payable in accordance with
their terms, or is intended to or shall affect the relative rights of the
Holders of the Subordinated Debentures and creditors of the Company, other than
the holders of Senior Indebtedness, nor shall anything herein or therein prevent
the Trustee or the Holder of any Subordinated Debenture from exercising all
remedies otherwise permitted by applicable law upon default under the Indenture,
subject to the rights, if any, under this Article Six of the holders of such
Senior Indebtedness in respect of cash, property or securities of the Company
received upon the exercise of any such remedy. Upon any payment or distribution
of assets of the Company referred to in this Article Six, the Trustee, subject
to the provisions of Section 602 of the Indenture, and the Holders of the
Subordinated Debentures shall be entitled to rely upon any order or decree made
by any court of

<PAGE>

competent jurisdiction in which such dissolution, winding-up, liquidation or
reorganization proceedings are pending, or a certificate of the receiver,
trustee in bankruptcy, liquidation trustee, agent or other Person making such
payment or distribution, delivered to the Trustee or to the Holders of the
Subordinated Debentures, for the purposes of ascertaining the Persons entitled
to participate in such distribution, the holders of Senior Indebtedness and
other indebtedness of the Company, the amount thereof or payable thereon, the
amount or amounts paid or distributed thereon and all other facts pertinent
thereto or to this Article Six.

     SECTION 6.5. Trustee to Effectuate Subordination.

     Each Holder of Subordinated Debentures by such Holder's acceptance thereof
authorizes and directs the Trustee on such Holder's behalf to take such action
as may be necessary or appropriate to effectuate the subordination provided in
this Article Six and appoints the Trustee such Holder's attorney-in-fact for any
and all such purposes.

     SECTION 6.6. Notice by the Company.

     The Company shall give prompt written notice to a Responsible Officer of
the Trustee of any fact known to the Company that would prohibit the making of
any payment of monies to or by the Trustee in respect of the Subordinated
Debentures pursuant to the provisions of this Article Six. Notwithstanding the
provisions of this Article Six or any other provision of the Indenture and this
Fourth Supplemental Indenture, the Trustee shall not be charged with knowledge
of the existence of any facts that would prohibit the making of any payment of
monies to or by the Trustee in respect of the Subordinated Debentures pursuant
to the provisions of this Article Six, unless and until a Responsible Officer of
the Trustee shall have received written notice thereof from the Company or a
holder or holders of Senior Indebtedness or from any trustee therefor; and
before the receipt of any such written notice, the Trustee, subject to the
provisions of Section 602 of the Indenture, shall be entitled in all respects to
assume that no such facts exist; PROVIDED, HOWEVER, that, if the Trustee shall
not have received the notice provided for in this Section 6.6 at least two
Business Days prior to the date upon which by the terms hereof any money may
become payable for any purpose (including, without limitation, the payment of
the principal of (or premium, if any) or interest on any Subordinated
Debenture), then, anything herein contained to the contrary notwithstanding, the
Trustee shall have full power and authority to receive such money and to apply
the same to the purposes for which they were received, and shall not be affected
by any notice to the contrary that may be received by it within two Business
Days prior to such date.

     The Trustee, subject to the provisions of Section 602 of the Indenture,
shall be entitled to rely on the delivery to it of a written notice by a Person
representing himself to be a holder of Senior Indebtedness (or a trustee on
behalf of such holder) to establish that such notice has been given by a holder
of such Senior Indebtedness or a trustee on behalf of any such holder or
holders. In the event that the Trustee determines in good faith that further
evidence is required with respect to the right of any Person as a holder of such
Senior Indebtedness to participate in any payment or distribution pursuant to
this Article Six, the Trustee may request such Person to furnish evidence to the
reasonable satisfaction of the Trustee as to the amount of such Senior
Indebtedness held by such Person, the extent to which such Person is entitled to
participate in such payment or distribution and any other facts pertinent to the
rights of such Person under this

<PAGE>

Article Six, and, if such evidence is not furnished, the Trustee may defer any
payment to such Person pending judicial determination as to the right of such
Person to receive such payment.

     SECTION 6.7. Rights of the Trustee; Holders of Senior Indebtedness.

     The Trustee in its individual capacity shall be entitled to all the rights
set forth in this Article Six in respect of any Senior Indebtedness at any time
held by it, to the same extent as any other holder of Senior Indebtedness, and
nothing in this Indenture shall deprive the Trustee of any of its rights as such
holder.

     With respect to the holders of Senior Indebtedness, the Trustee undertakes
to perform or to observe only such of its covenants and obligations as are
specifically set forth in this Article Six, and no implied covenants or
obligations with respect to the holders of such Senior Indebtedness shall be
read into this Indenture against the Trustee. The Trustee shall not be deemed to
owe any fiduciary duty to the holders of such Senior Indebtedness, and the
Trustee shall not be liable to any holder of such Senior Indebtedness if it
shall mistakenly pay over or deliver to the Holders of the Subordinated
Debentures, the Company or any other Person money or assets to which any holder
of such Senior Indebtedness shall be entitled by virtue of this Article Six or
otherwise.

     SECTION 6.8. Subordination May Not Be Impaired.

     No right of any present or future holder of any Senior Indebtedness to
enforce subordination as herein provided shall at any time in any way be
prejudiced or impaired by any act or failure to act on the part of the Company
or by any act or failure to act, in good faith, by any such holder, or by any
noncompliance by the Company with the terms, provisions and covenants of the
Indenture, regardless of any knowledge thereof that any such holder may have or
otherwise be charged with. Without in any way limiting the generality of the
foregoing paragraph, the holders of Senior Indebtedness may, at any time and
from time to time, without the consent of or notice to the Trustee or the
Holders of the Subordinated Debentures, without incurring responsibility to the
Holders of the Subordinated Debentures and without impairing or releasing the
subordination provided in this Article Six or the obligations hereunder of the
Holders of the Subordinated Debentures to the holders of such Senior
Indebtedness, do any one or more the following: (i) change the manner, place or
terms of payment or extend the time of payment of, or renew or alter, such
Senior Indebtedness, or otherwise amend or supplement in any manner such Senior
Indebtedness or any instrument evidencing the same or any agreement under which
such Senior Indebtedness is outstanding; (ii) sell, exchange, release or
otherwise deal with any property pledged, mortgaged or otherwise securing such
Senior Indebtedness; (iii) release any Person liable in any manner for the
collection of such Senior Indebtedness; and (iv) exercise or refrain from
exercising any rights against the Company and any other Person.

<PAGE>

                                   ARTICLE VII
                                    COVENANTS

     SECTION 7.1. Covenants.

     (a) If Subordinated Debentures are to be distributed to the holders of the
Preferred Securities upon a Dissolution Event, the Company will use its best
efforts to list such Subordinated Debentures on the New York Stock Exchange or
on such other exchange as the Preferred Securities are then listed.

     (b) The Company shall maintain directly or indirectly 100% ownership of the
Common Securities, provided that certain successors that are permitted pursuant
to the Indenture may succeed to the Company's ownership of the Common
Securities;

     (c) The Company will not voluntarily dissolve, wind up or liquidate the
Trust, except

          (i)  in connection with a distribution of the Subordinated Debentures
               to the holders of the Preferred Securities in liquidation of the
               Trust; or

          (ii) in connection with certain mergers, consolidations or
               amalgamations permitted by the Declaration, and

     (d) The Company shall use reasonable efforts, consistent with the terms and
provisions of the Declaration, to cause the Trust to remain classified as a
grantor trust and not as an association taxable as a corporation for United
States federal income tax purposes.

                                  ARTICLE VIII
                         FORM OF SUBORDINATED DEBENTURE

     SECTION 8.1. Form of Subordinated Debenture.

     The Subordinated Debentures and the Trustee's Certificate of Authentication
to be endorsed thereon are to be substantially in the following forms:

                           (FORM OF FACE OF DEBENTURE)

     [IF THE DEBENTURE IS TO BE A GLOBAL DEBENTURE, INSERT: This Subordinated
Debenture is a Global Debenture within the meaning of the Indenture hereinafter
referred to and is registered in the name of a Depository or a nominee of a
Depository. This Subordinated Debenture is exchangeable for Subordinated
Debentures registered in the name of a person other than the Depository or its
nominee only in the limited circumstances described in the Indenture, and no
transfer of this Subordinated Debenture (other than a transfer of this
Subordinated Debenture as a whole by the Depository to a nominee of the
Depository or by a nominee of the Depository to the Depository or another
nominee of the Depository) may be registered except in limited circumstances.
Unless this Subordinated Debenture is presented by an authorized representative
of The Depository Trust Company (55 Water Street, New York,

<PAGE>

New York) to the issuer or its agent for registration of transfer, exchange or
payment, and any Subordinated Debenture issued is registered in the name of Cede
& Co. or such other name as requested by an authorized representative of The
Depository Trust Company and any payment hereon is made to Cede & Co., ANY
TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY A PERSON IS
WRONGFUL since the registered owner hereof, Cede & Co., has an interest herein.]



No.                                                       $
    ---------                                              --------------------
                                                            CUSIP No. 668074AE7

             8.10% JUNIOR SUBORDINATED DEFERRABLE INTEREST DEBENTURE
                              DUE JANUARY 15, 2032

     NorthWestern Corporation, a Delaware corporation (the "Company", which term
includes any successor corporation under the Indenture hereinafter referred to),
for value received, hereby promises to pay to _________________________, or
registered assigns, the principal sum of ________________________ on January 15,
2032, and to pay interest on said principal sum from January 31, 2002, or from
the most recent interest payment date (each such date, an "Interest Payment
Date") to which interest has been paid or duly provided for, quarterly (subject
to deferral as set forth herein) in arrears on January 15, April 15, July 15 and
October 15 of each year commencing April 15, 2002, at the rate of 8.10% per
annum until the principal hereof shall have become due and payable, and on any
overdue principal and premium, if any, and (without duplication and to the
extent that payment of such interest is enforceable under applicable law) on any
overdue installment of interest at the same rate per annum compounded quarterly.
The amount of interest payable on any Interest Payment Date shall be computed on
the basis of a 360-day year of twelve 30-day months. In the event that any date
on which interest is payable on this Subordinated Debenture is not a Business
Day, then payment of interest payable on such date will be made on the next
succeeding day that is a Business Day (and without any interest or other payment
in respect of any such delay), except that, if such Business Day is in the next
succeeding calendar year, such payment shall be made on the immediately
preceding Business Day, in each case with the same force and effect as if made
on such date. The interest installment so payable, and punctually paid or duly
provided for, on any Interest Payment Date will, as provided in the Indenture,
be paid to the person in whose name this Subordinated Debenture (or one or more
Predecessor Securities, as defined in said Indenture) is registered at the close
of business on the Regular Record Date for such interest installment, which, if
this Subordinated Debenture is held by the Property Trustee or is a Global
Debenture, shall be the close of business on the Business Day next preceding
such Interest Payment Date or, if the Preferred Securities are no longer in
book-entry only form or this Subordinated Debenture is not a Global Debenture,
shall be 15 Business Days before the relevant Interest Payment Date; provided
that interest paid at maturity shall be paid to the Person to whom principal is
paid. Any such interest installment not punctually paid or duly provided for
shall forthwith cease to be payable to the registered Holders on such Regular
Record Date and may be paid to the Person in whose name this Subordinated
Debenture (or one or more Predecessor Securities) is registered at the close of
business on a special record date to be fixed by the Trustee for the payment of
such

<PAGE>

defaulted interest, notice whereof shall be given to the registered Holders of
the Subordinated Debentures not less than 10 days prior to such special record
date, or may be paid at any time in any other lawful manner not inconsistent
with the requirements of any securities exchange on which the Subordinated
Debentures may be listed, and upon such notice as may be required by such
exchange, all as more fully provided in the Indenture. The principal of (and
premium, if any) and interest on this Subordinated Debenture shall be payable at
the office or agency of the Trustee maintained for that purpose in any coin or
currency of the United States of America that at the time of payment is legal
tender for payment of public and private debts; PROVIDED, HOWEVER, that payment
of interest may be made at the option of the Company by check mailed to the
registered Holder at such address as shall appear in the Security Register.
Notwithstanding the foregoing, so long as the Holder of this Subordinated
Debenture is the Property Trustee, the payment of the principal of (and premium,
if any) and interest on this Subordinated Debenture will be made at such place
and to such account as may be designated by the Property Trustee.

     The indebtedness evidenced by this Subordinated Debenture is, to the extent
provided in the Indenture, subordinate and junior in right of payment to the
prior payment in full of all Senior Indebtedness, and this Subordinated
Debenture is issued subject to the provisions of the Indenture with respect
thereto. Each Holder of this Subordinated Debenture, by accepting the same, (a)
agrees to and shall be bound by such provisions, (b) authorizes and directs the
Trustee on his or her behalf to take such action as may be necessary or
appropriate to acknowledge or effectuate the subordination so provided and (c)
appoints the Trustee his or her attorney-in-fact for any and all such purposes.
Each Holder hereof, by his or her acceptance hereof, hereby waives all notice of
the acceptance of the subordination provisions contained herein and in the
Indenture by each holder of Senior Indebtedness, whether now outstanding or
hereafter incurred, and waives reliance by each such holder upon said
provisions.

     Unless the Certificate of Authentication hereon has been executed by the
Trustee referred to on the reverse side hereof, this Subordinated Debenture
shall not be entitled to any benefit under the Indenture or be valid or
obligatory for any purpose.

     The provisions of this Subordinated Debenture are continued on the reverse
side hereof, and such continued provisions shall for all purposes have the same
effect as though fully set forth at this place.



<PAGE>


     IN WITNESS WHEREOF, the Company has caused this instrument to be executed.

Dated:   _______ __, 2002
                                         NORTHWESTERN CORPORATION


                                         By: _________________________________
                                             Name:
                                             Title:
Attest:


By:      __________________________
         Assistant Secretary


                          CERTIFICATE OF AUTHENTICATION

     This is one of the Securities of the series designated therein referred to
in the within-mentioned Indenture.

Dated:  ________ __, 2002                JPMorgan Chase Bank, as Trustee


                                          By: __________________________
                                              Authorized Officer


<PAGE>


                         (FORM OF REVERSE OF DEBENTURE)

     This Subordinated Debenture is one of a duly authorized series of
Securities of the Company (herein sometimes referred to as the "Subordinated
Debentures"), all issued under and pursuant to an Indenture, dated as of August
1, 1995, duly executed and delivered between the Company and JPMorgan Chase Bank
(as successor to The Chase Manhattan Bank), as Trustee (the "Trustee"), as
supplemented by the First Supplemental Indenture thereto, dated as of August 1,
1995 and as further supplemented by the Second Supplemental Indenture thereto,
dated as of November 15, 1998, as further supplemented by the Third Supplemental
Indenture thereto, dated as of December 21, 2001 and as further supplemented by
the Fourth Supplemental Indenture thereto, dated as of January 31, 2002 between
the Company and the Trustee (such Indenture as so supplemented, the
"Indenture"), to which Indenture and all indentures supplemental thereto
reference is hereby made for a description of the rights, limitations of rights,
obligations, duties and immunities thereunder of the Trustee, the Company and
the Holders of the Subordinated Debentures. By the terms of the Indenture, the
Securities are issuable in series that may vary as to amount, date of maturity,
rate of interest and in other respects as provided in the Indenture. This series
of Securities is limited in aggregate principal amount to $103,092,800;
PROVIDED, HOWEVER, if the Overallotment Option is exercised, the aggregate
principal amount may be increased to up to $118,556,725.

     The Company shall have the right to redeem this Subordinated Debenture at
the option of the Company, without premium or penalty, (i) in whole or in part
at any time on or after January 31, 2007 and (ii) in whole (but not in part) at
any time before January 31, 2007 in certain circumstances upon the occurrence of
a Tax Event or an Investment Company Event, in each case at a redemption price
equal to 100% of the principal amount plus any accrued but unpaid interest
hereon to the date of such redemption (the "Redemption Price"). Any redemption
pursuant to this paragraph will be made upon not less than 30 nor more than 60
days' notice, at the Redemption Price. The Company may not redeem fewer than all
of the Subordinated Debentures unless all accrued and unpaid interest has been
paid on all Subordinated Debentures for all quarterly interest payment periods
terminating on or prior to the date of redemption. If a partial redemption of
the Subordinated Debentures would result in the delisting of the Preferred
Securities issued by the Trust from any national securities exchange or other
organization on which the Preferred Securities are then listed, the Company
shall not be permitted to effect such partial redemption and may only redeem the
Subordinated Debentures in whole. If the Subordinated Debentures are only
partially redeemed by the Company, the particular Subordinated Debentures to be
redeemed will be selected on a pro rata basis by such method as the Trustee
shall deem fair and appropriate or, if the Subordinated Debentures are
registered as a Global Debenture, in accordance with the Depository's customary
procedures.

     In the event of redemption of this Subordinated Debenture in part only, a
new Subordinated Debenture or Debentures for the unredeemed portion hereof will
be issued in the name of the Holder hereof upon the cancellation hereof.

     In case an Event of Default, as defined in the Indenture, shall have
occurred and be continuing, the principal of all of the Subordinated Debentures
may be declared, and upon such declaration shall become, due and payable, in the
manner, with the effect and subject to the conditions provided in the Indenture.


                                      -2-
<PAGE>


     The Indenture contains provisions permitting the Company and the Trustee,
with the consent of the Holders of not less than a majority in aggregate
principal amount of the Subordinated Debentures and all other series of
Securities affected at the time Outstanding, as defined in the Indenture, to
execute supplemental indentures for the purpose of adding any provisions to or
changing in any manner or eliminating any of the provisions of the Indenture or
of any supplemental indenture or of modifying in any manner the rights of the
Holders of the Subordinated Debentures; PROVIDED, HOWEVER, that no such
supplemental indenture may, without the consent of the Holder of each
outstanding Subordinated Debenture, among other things, (i) change the stated
maturity of the principal of, or any installment of interest on, any
Subordinated Debenture, (ii) reduce the principal amount of, or the rate of
interest on or any Additional Sums payable in respect of, or any premium payable
upon the redemption of, the Subordinated Debentures, or change the redemption
provisions of the Subordinated Debentures, (iii) impair the right to institute
suit for the enforcement of any such payment on or after the stated maturity of
or any redemption date for the Subordinated Debentures or (iv) reduce the
above-stated percentage of principal amount of Subordinated Debentures, the
Holders of which are required to modify or amend the Indenture, to consent to
any waiver thereunder or to approve any supplemental indenture. The Indenture
also contains provisions permitting the Holders of a majority in aggregate
principal amount of the Subordinated Debentures at the time outstanding affected
thereby, on behalf of all of the Holders of the Subordinated Debentures, to
waive any past default in the performance of any of the covenants contained in
the Indenture, or established pursuant to the Indenture with respect to the
Subordinated Debentures, and its consequences, except a default in the payment
of the principal of or interest on any of the Subordinated Debentures (unless
cured as provided in the Indenture) or in respect of a covenant or provision
that cannot be modified or amended without the consent of the Holders of each
Subordinated Debenture then outstanding. Any such consent or waiver by the
registered Holder of this Subordinated Debenture (unless revoked as provided in
the Indenture) shall be conclusive and binding upon such Holder and upon all
future Holders and owners of this Subordinated Debenture and of any Subordinated
Debenture issued in exchange herefor or in place hereof (whether by registration
of transfer or otherwise), irrespective of whether or not any notation of such
consent or waiver is made upon this Subordinated Debenture.

     No reference herein to the Indenture and no provision of this Subordinated
Debenture or of the Indenture shall alter or impair the obligation of the
Company, which is absolute and unconditional, to pay the principal of and
premium, if any, and interest on this Subordinated Debenture at the time and
place and at the rate and in the money herein prescribed.

     So long as no Event of Default has occurred and is continuing, the Company
shall have the right at any time during the term of this Subordinated Debenture
from time to time to extend the interest payment period hereof to up to 20
consecutive quarters, but not beyond the Maturity Date of this Subordinated
Debenture (an "Extended Interest Payment Period"), at the end of which period
the Company shall pay all interest then accrued and unpaid (together with
interest thereon at the rate specified herein to the extent that payment of such
interest is enforceable under applicable law).

     Before the termination of any such Extended Interest Payment Period, the
Company may further extend such Extended Interest Payment Period, provided that
such Extended Interest Payment Period together with all such previous and
further extensions thereof shall not exceed


                                      -3-
<PAGE>

20 consecutive quarters or extend beyond the Maturity Date. At the termination
of any such Extended Interest Payment Period and upon the payment of all accrued
and unpaid interest and any additional amounts then due, the Company may
commence a new Extended Interest Payment Period.

     As provided in the Indenture and subject to certain limitations therein set
forth, this Subordinated Debenture is transferable by the registered Holder
hereof on the Security Register of the Company, upon surrender of this
Subordinated Debenture for registration of transfer at the office or agency of
the Company in the City and State of New York accompanied by a written
instrument or instruments of transfer in form satisfactory to the Company or the
Trustee duly executed by the registered Holder hereof or his attorney duly
authorized in writing, and thereupon one or more new Subordinated Debentures of
authorized denominations and for the same aggregate principal amount will be
issued to the designated transferee or transferees. No service charge will be
made for any such transfer, but the Company may require payment of a sum
sufficient to cover any tax or other governmental charge payable in relation
thereto.

     Prior to due presentment for registration of transfer of this Subordinated
Debenture, the Company, the Trustee, any paying agent and any Security Registrar
may deem and treat the registered holder hereof as the absolute owner hereof
(whether or not this Subordinated Debenture shall be overdue and notwithstanding
any notice of ownership or writing hereon made by anyone other than the Security
Registrar) for the purpose of receiving payment of or on account of the
principal hereof and premium, if any, and interest due hereon and for all other
purposes, and neither the Company nor the Trustee nor any paying agent nor any
Security Registrar shall be affected by any notice to the contrary.

     No recourse shall be had for the payment of the principal of or the
interest on this Subordinated Debenture, or for any claim based hereon, or
otherwise in respect hereof, or based on or in respect of the Indenture, against
any incorporator, stockholder, officer or director, past, present or future, as
such, of the Company or of any predecessor or successor corporation, whether by
virtue of any constitution, statute or rule of law, or by the enforcement of any
assessment or penalty or otherwise, all such liability being, by the acceptance
hereof and as part of the consideration for the issuance hereof, expressly
waived and released.

     The Subordinated Debentures of this series are issuable only in registered
form without coupons in denominations of $25 and any integral multiple thereof.
As provided in the Indenture and subject to certain limitations herein and
therein set forth, Subordinated Debentures of this series so issued are
exchangeable for a like aggregate principal amount of Subordinated Debentures of
this series of a different authorized denomination, as requested by the Holder
surrendering the same.

     All terms used in this Subordinated Debenture that are defined in the
Indenture shall have the meanings assigned to them in the Indenture.


                                      -4-
<PAGE>


                                   ARTICLE IX
                    ORIGINAL ISSUE OF SUBORDINATED DEBENTURES

     SECTION 9.1. Original Issue of Subordinated Debentures.

     Subordinated Debentures may, upon execution of this Fourth Supplemental
Indenture, be executed by the Company and delivered to the Trustee for
authentication, and the Trustee shall thereupon authenticate and deliver said
Subordinated Debentures to or upon receipt of a Company Order, without any
further action by the Company.

                                   ARTICLE X
                    RIGHTS OF HOLDERS OF PREFERRED SECURITIES

     SECTION 10.1. Preferred Security Holders' Rights.

     Notwithstanding Section 507 of the Indenture, if the Property Trustee fails
to enforce its rights under the Declaration or the Subordinated Debentures, any
holder of Preferred Securities may institute a legal proceeding against the
Company to enforce the Property Trustee's rights under the Declaration or the
Subordinated Debentures without first instituting any legal proceeding against
the Property Trustee or any other Person or entity.

     SECTION 10.2. Direct Action.

     Notwithstanding any other provision of the Indenture, for as long as any
Preferred Securities remain outstanding, to the fullest extent permitted by law,
if an Event of Default has occurred and is continuing and such event is
attributable to the failure of the Company to pay interest or principal on the
Subordinated Debentures on the date such interest or principal is due and
payable, any holder of Preferred Securities shall have the right to institute a
proceeding directly against the Company for enforcement of payment to such
holder of the principal of or interest (including any Compounded Interest or
Additional Sums) on Subordinated Debentures having an aggregate principal amount
equal to the aggregate liquidation amount of such holder's Preferred Securities
(a "Direct Action"). The Company may not amend this Subordinated Indenture to
remove the right to bring a Direct Action without the prior written consent of
the holders of all the Preferred Securities then outstanding.

     SECTION 10.3. Payments Pursuant to Direct Actions.

     The Company shall have the right to set-off against its obligations to the
Trust, as Holder of the Subordinated Debentures, any payment made to a holder of
Preferred Securities in connection with a Direct Action.


                                      -5-
<PAGE>


                                   ARTICLE XI
                                  MISCELLANEOUS

     SECTION 11.1. Ratification of Indenture.

     The Indenture, as heretofore supplemented and as further supplemented by
this Fourth Supplemental Indenture, is in all respects ratified and confirmed,
and this Fourth Supplemental Indenture shall be deemed part of the Indenture in
the manner and to the extent herein and therein provided.

     SECTION 11.2. Trustee Not Responsible for Recitals.

     The recitals herein contained are made by the Company and not by the
Trustee, and the Trustee assumes no responsibility for the correctness thereof.
The Trustee makes no representation as to the validity or sufficiency of this
Fourth Supplemental Indenture.

     SECTION 11.3. Governing Law.

     This Fourth Supplemental Indenture and each Subordinated Debenture shall be
deemed to be a contract made under the internal laws of the State of New York
and for all purposes shall be construed in accordance with the laws of said
State.

     SECTION 11.4. Separability.

     In case any one or more of the provisions contained in this Fourth
Supplemental Indenture or in the Subordinated Debentures shall for any reason be
held to be invalid, illegal or unenforceable in any respect, such invalidity,
illegality or unenforceability shall not affect any other provisions of this
Fourth Supplemental Indenture or of the Subordinated Debentures, but this Fourth
Supplemental Indenture and the Subordinated Debentures shall be construed as if
such invalid or illegal or unenforceable provision had never been contained
herein or therein.

     SECTION 11.5. Counterparts.

     This Fourth Supplemental Indenture may be executed in any number of
counterparts each of which shall be an original; but such counterparts shall
together constitute but one and the same instrument.

     SECTION 11.6. Overallotment Option.

     This Fourth Supplemental Indenture shall permit the issuance from time to
time, subject to the terms of the Overallotment Option, of additional
Subordinated Debentures of this series in accordance with the procedures
established in Section 303 of the Indenture.


                                      -6-
<PAGE>



     IN WITNESS WHEREOF, the parties hereto have caused this Fourth Supplemental
Indenture to be duly executed, and their respective corporate seals to be
hereunto affixed and attested, on the date or dates indicated in the
acknowledgments and as of the day and year first above written.

                                           NORTHWESTERN CORPORATION


                                           By:      /s/ Richard R. Hylland
                                                    ---------------------------
                                           Name:    Richard R. Hylland
                                           Title:   President and Chief
                                                    Operating Officer


Attest:  /s/ Alan D. Dietrich
         ------------------------------
Name:    Alan D. Dietrich
Title:   Corporate Secretary


                                           JPMORGAN CHASE BANK


                                           By:  /s/ R.J. Halleran
                                                ---------------------------
                                           Name:  R.J. Halleran
                                           Title: Assistant Vice President



Attest:  /s/ M. Kearney
         -------------------------------
Name:    M. Kearney
Title:   Corporate Secretary



<PAGE>


STATE OF SOUTH DAKOTA      )
                           )  SS
COUNTY OF MINNEHAHA        )


     On the 31st day of January, 2002, before me personally Richard R.
Hylland and came to be known, who, being by me duly sworn, did depose and say
that he is the President and Chief Operating Officer of NorthWestern
Corporation, one of the corporations described in and which executed the above
instrument; that he knows the corporate seal of said corporation; that the seal
affixed to the said instrument is such corporation seal; that it was so affixed
by authority of the Board of Directors of said corporation, and that he signed
his name thereto by like authority.

     IN WITNESS WHEREOF, I have hereunto set my hand and affixed my seal of
office this 31st day of January, 2002.


                                             /s/ Alan Dietrich
                                    -------------------------------------
(Notarial Seal)                                 Alan Dietrich
                                    NOTARY PUBLIC, MINNEHAHA COUNTY, S.D.
                                     My Commission Expires March 30, 2009


STATE OF NEW YORK          )
                           )  SS
COUNTY OF NEW YORK         )


     On the 31st day of January, 2002, before me personally R.J. Halleran
came to be known, who, being by me duly sworn, did depose and say that he is
the Assistant Vice President of JPMorgan Chase Bank, one of the corporations
described in and which executed the above instrument; that he knows the
corporate seal of said corporation; that the seal affixed to the said
instrument is such corporation seal; that it was so affixed by authority of
the Board of Directors of said corporation, and that he signed his name
thereto by like authority.

     IN WITNESS WHEREOF, I have hereunto set my hand and affixed my seal of
office this 31st day of January, 2002.

                                                  /s/ Emily Fayan
(Notarial Seal)                         ---------------------------------------
                                          NOTARY PUBLIC, KINGS COUNTY, N.Y.
                                        My Commission Expires December 31, 2005