When Recorded
      Mail To:James A.
      TisckosCentral
      Illinois Public Service Company607 East
      Adams StreetSpringfield,
      IL 62739







Executed in 100
Counterparts, No.  .




Supplemental
Indenture




dated
October 1, 2004




Central
Illinois Public Service Company




to




U.S.
Bank National Association




and
Patrick J. Crowley,


as
trustees




(Supplemental
to the Indenture of Mortgage or Deed of Trust


dated
October 1, 1941, executed by Central Illinois Public Service Company


to
Continental Illinois National Bank and Trust Company of Chicago


and
Edmond B. Stofft, as trustees)


(Providing
for First Mortgage Bonds, Environmental Improvement Series 2004)








This instrument was
prepared by Steven R. Sullivan, Senior Vice President Governmental/Regulatory
Policy, General Counsel and Secretary of Central Illinois Public Service
Company, One Ameren Plaza, 1901 Chouteau Avenue, St. Louis, Missouri
63103.








This Supplemental
Indenture, dated
October 1, 2004, made and entered into by and between Central Illinois
Public Service Company , a corporation
organized and existing under the laws of the State of Illinois (hereinafter
commonly referred to as the *“Company”* ), and U.S. Bank
National Association (formerly U.S.
Bank Trust National Association, formerly First Trust National Association,
formerly First Trust of Illinois, National Association, successor trustee to
Bank of America Illinois, formerly Continental Bank, formerly Continental Bank,
National Association and formerly Continental Illinois National Bank and Trust
Company of Chicago), a national banking association having its office or place
of business in the City of Chicago, Cook County, State of Illinois (hereinafter
commonly referred to as the *“Trustee”* ), and Patrick J.
Crowley (successor Co-Trustee), of the City of Montvale, Bergen County, State of
New Jersey, as Trustees under the Indenture of Mortgage or Deed of Trust dated
October 1, 1941, heretofore executed and delivered by the Company to
Continental Illinois National Bank and Trust Company of Chicago and Edmond B.
Stofft, as Trustees, as amended by the Supplemental Indentures dated,
respectively, September 1, 1947, January 1, 1949, February 1,
1952, September 1, 1952, June 1, 1954, February 1, 1958,
January 1, 1959, May 1, 1963, May 1, 1964, June 1, 1965,
May 1, 1967, April 1, 1970, April 1, 1971, September 1,
1971, May 1, 1972, December 1, 1973, March 1, 1974, April 1,
1975, October 1, 1976, November 1, 1976, October 1, 1978,
August 1, 1979, February 1, 1980, February 1, 1986, May 15,
1992, July 1, 1992, September 15, 1992, April 1, 1993, June 1,
1995, March 15, 1997, June 1, 1997, December 1, 1998 and
June 1, 2001, heretofore executed and delivered by the Company to the
Trustees under said Indenture of Mortgage or Deed of Trust dated October 1,
1941; said Indenture of Mortgage or Deed of Trust dated October 1, 1941, as
amended by said Supplemental Indentures, being hereinafter sometimes referred to
as the *“Indenture”* ; and said U.S.
Bank National Association and Patrick J. Crowley, as such Trustees, being
hereinafter sometimes referred to as the *“Trustees”* or the *“Trustees under
the Indenture”* ;




**Witnesseth:**




Whereas , the Company has
determined, by resolutions duly adopted by its Board of Directors, to issue
bonds of an additional series under and to be secured by the Indenture, as
hereby amended, to be known and designated as First Mortgage Bonds,
Environmental Improvement Series 2004 (hereinafter sometimes referred to as
the *“bonds of
Environmental Improvement Series 2004”* or the *“bonds of said
Series”* ), and the bonds of
said Series shall be authorized, authenticated and issued only as registered
bonds without coupons, and to execute and deliver this supplemental indenture,
pursuant to the provisions of Article I, as amended, Section 6 of
Article II and Article XVI of the Indenture, for the purpose of
(1) creating and authorizing not to exceed $35,000,000 aggregate principal
amount of bonds of Environmental Improvement Series 2004 and setting forth
the form, terms, provisions and characteristics thereof, (2) modifying or
amending certain provisions of the Indenture in the particulars and to the
extent hereinafter specifically provided, and (3) specifically describing
and conveying to the Trustees, upon the trusts and for the purposes of the
Indenture, as hereby amended, certain additional properties which the Company
has constructed or otherwise acquired subsequent to March 31, 2001, except
property of the character expressly excepted or excluded from the lien of the
Indenture by the terms thereof, and which are owned by the Company at the date
of the execution hereof and are subject in any event to the lien and effect of
the Indenture; and




Whereas , the Illinois
Finance Authority (the *“Authority”* ) has agreed to
issue $35,000,000 in principal amount of its Environmental Improvement Revenue
Refunding Bonds (AmerenCIPS Project) Series 2004 (the *“Revenue
Refunding Bond Series 2004”* ), pursuant to the
provisions of an Indenture of Trust dated as of October 1, 2004 (the *“Series 2004
Trust Indenture”* ) between the
Authority and UMB Bank, N.A., as Trustee (said Trustee, or any successor trustee
under the Series 2004 Trust Indenture, being hereinafter referred to as the *“Trust
Indenture Trustee”* ); and




Whereas , the proceeds of
the Revenue Refunding Bonds Series 2004 will be loaned by the Authority to
the Company pursuant to a Loan Agreement dated as of October 1, 2004 (the *“Series 2004
Loan Agreement”* ) between the
Authority and the Company, in order to finance the refunding of outstanding
obligations incurred to finance a portion of the costs of certain pollution
control facilities at the Coffeen and Newton coal fired electric generating
stations located in the Illinois counties of Montgomery and Jasper,
respectively, which stations are now owned by Ameren Energy Generating Company,
an affiliate of the Company, and which facilities are described in Exhibit A to
the Series 2004 Loan Agreement; and




Whereas , payments to be
made by the Company pursuant to the Series 2004 Loan Agreement have been
assigned by the Authority to the Trust Indenture Trustee in order to secure the
payment of the Revenue Refunding Bonds Series 2004; and




Whereas , in order to
secure the Company’s loan payment obligations under the Series 2004 Loan
Agreement and to provide for the payment of principal, interest and premium, if
any, in respect of the Revenue Refunding Bonds Series 2004, and in order to
comply with the provisions of Section 4.08 of the Series 2004 Loan
Agreement, the Company desires to issue its bonds of Environmental Improvement
Series 2004 to the Trust Indenture Trustee in a principal amount equal to
the principal amount of the Revenue Refunding Bonds Series 2004; and




Whereas , the execution and
delivery by the Company of this supplemental indenture have been duly authorized
by the Board of Directors of the Company; and the Company has requested, and
hereby requests, the Trustees to enter into and join with the Company in the
execution and delivery of this supplemental indenture; and




Whereas , the bonds of
Environmental Improvement Series 2004 to be authorized, authenticated and
issued only in the form of registered bonds without coupons, and the bonds of
Environmental Improvement Series 2004 and the certificate of the Trustee
thereon shall be substantially in the following form, to wit:













**[FORM OF
BOND]**





No.
_______ $__________





Illinois Commerce
Commission


Identification No.:
Ill. C.C. No. 6337





**Notwithstanding
any provisions hereof or in the Indenture**


**this Bond
is not assignable or transferable except as**


**permitted
or required by Section 13.15 of the Indenture of
Trust,**


**dated as of
October 1, 2004, hereinafter referred to.**





Central Illinois
Public Service Company


First Mortgage
Bond, Environmental Improvement Series 2004











Original
      Issue
      Date
    Dated
      Date*
    Maturity
      Date
    CUSIPJuly 1,
      2025




REGISTERED
OWNER 
____________________________________________________________________________________________________




PRINCIPAL
AMOUNT ___________________________________________________________________________________________DOLLARS








Central Illinois
Public Service Company, an Illinois corporation (hereinafter referred to as the *“Company”* ), for value
received, hereby promises to pay to the Registered Owner specified above, as
trustee under the Series 2004 Trust Indenture hereinafter referred to, or
registered assigns, the Principal Amount specified above on the Maturity Date
specified above, subject to prior redemption and to pay to the Registered Owner
interest on said sum from the Dated Date hereof, at the same interest rate or
rates and on the same dates as the Revenue Refunding Bonds Series 2004
(hereinafter referred to) (as determined in accordance with the Series 2004
Trust Indenture referred to above), until said principal sum is paid, but in no
event shall the interest rate exceed eighteen percent (18%) per annum. The
interest so payable on any interest payment date will be paid, subject to
certain exceptions provided in the Supplemental Indenture dated October 1,
2004, hereinafter referred to, to the Registered Owner at the close of business
of the Trustee hereinafter referred to on the business day immediately preceding
the interest payment date. Both the principal of and the interest on this bond
shall be payable in immediately available funds at the office or agency of the
Trust Indenture Trustee hereinafter





___________________


*To be completed in
accordance with the terms of Section 1.1 of Article I
hereof.








referred to,
in any coin or currency of the United States of America which at the time of
payment is legal tender for public and private debts.




Under an Indenture
of Trust dated as of October 1, 2004 (the *“Series 2004
Trust Indenture”* ) between the
Illinois Finance Authority (the *“Authority”* ) and UMB Bank,
N.A., as trustee (the *“Trust
Indenture Trustee”* ), the Authority
will issue, concurrently with the issuance of this bond, an issue of Bonds under
the Series 2004 Trust Indenture entitled “Environmental Improvement Revenue
Refunding Bonds (AmerenCIPS Project) Series 2004” (the *“Revenue
Refunding Bonds Series 2004”* ). The proceeds of
the Revenue Refunding Bonds Series 2004 will be loaned by the Authority to
the Company pursuant to a Loan Agreement dated as of October 1, 2004 (the *“Series 2004
Loan Agreement”* ) between the
Authority and the Company. Pursuant to Section 4.08 of the Series 2004
Loan Agreement, this bond is issued to the Trust Indenture Trustee to secure any
and all obligations of the Company under the Series 2004 Loan Agreement
relating to the Revenue Refunding Bonds Series 2004. Payment of principal
of, or premium, if any or interest on, the Revenue Refunding Bonds
Series 2004 shall constitute payments on this bond as further provided
herein and in the Supplemental Indenture dated October 1, 2004 pursuant to
which this bond has been issued (the *“Supplemental
Indenture”* ).




Upon any payment of
the principal of, premium, if any, and interest on, all or any portion of the
Revenue Refunding Bonds Series 2004, whether at maturity or prior to
maturity by redemption or otherwise or upon provision for the payment thereof
having been made in accordance with Section 8.01 of the Series 2004
Trust Indenture, bonds of Environmental Improvement Series 2004 in a
principal amount equal to the principal amount of such Revenue Refunding Bonds
Series 2004 and having both a corresponding maturity date and interest rate
shall, to the extent of such payment of principal, premium, if any, and
interest, be deemed paid and the obligation of the Company thereunder to make
such payment shall be discharged to such extent and, in the case of the payment
of principal (and premium, if any), such bonds shall be surrendered to the
Trustee (as hereinafter defined) for delivery to the Company for cancellation as
provided in Section 8.02 of the Series 2004 Trust Indenture. The
Trustee may at anytime and all times conclusively assume that the obligation of
the Company to make payments with respect to the principal of and premium, if
any, and interest on the Revenue Refunding Bonds Series 2004, so far as
such payments at the time have become due, has been fully satisfied and
discharged pursuant to the foregoing sentence unless and until the Trustee shall
have received a written notice from the Trust Indenture Trustee signed by one of
its officers stating (i) that timely payment of principal, or premium or
interest on, the Revenue Refunding Bonds Series 2004 has not been made,
(ii) that the Company is in arrears as to the payments required to be made
by it to the Trust Indenture Trustee pursuant to the Series 2004 Trust
Indenture, and (iii) the amount of the arrearage.




This bond is one of
the bonds issued and to be issued from time to time under and in accordance with
and all secured by the indenture of mortgage or deed of trust dated
October 1, 1941, executed and delivered by the Company to U.S. Bank
National Association (formerly U.S. Bank Trust National Association, formerly
First Trust National Association, formerly First Trust of Illinois, National
Association, successor trustee to Bank of America Illinois, formerly Continental
Bank, formerly Continental Bank, National Association and formerly Continental
Illinois National Bank and Trust Company of Chicago and hereinafter referred to
as the *“Trustee”* ) and Edmond B.
Stofft, as Trustees, and the various indentures supplemental thereto, including
the Supplemental Indenture pursuant to which $35,000,000 in aggregate principal
amount of the First Mortgage Bonds, Environmental Improvement Series 2004
are authorized, each executed and delivered by the Company to the Trustees under
said indenture of mortgage or deed of trust dated October 1, 1941, prior to
the authentication of this bond (said indenture of mortgage or deed of trust and
said supplemental indentures being hereinafter referred to, collectively, as the *“Indenture”* ); and said U.S.
Bank National Association and Patrick J. Crowley (successor Co-Trustee)
being now the Trustees under the Indenture. Reference to the Indenture and to
all supplemental indentures, if any, hereafter executed pursuant to the
Indenture is hereby made for a description of the property mortgaged and
pledged, the nature and extent of the security and the rights of the holders and
Registered Owners of said bonds and of the Trustees and of the Company in
respect of such security. By the terms of the Indenture the bonds to be secured
thereby are issuable in series, which may vary as to date, amount, date of
maturity, rate of interest, redemption provisions, medium of payment and in
other respects as in the Indenture provided.




This bond is not
redeemable except on the respective dates, in the respective principal amounts
and for the respective redemption prices that correspond to the redemption dates
for, the principal amounts to be redeemed of, and the redemption prices for, the
Revenue Refunding Bonds Series 2004, and except upon written demand of the
Trust Indenture Trustee following the occurrence of an Event of Default under
the Series 2004 Trust Indenture and the acceleration of the Revenue
Refunding Bonds Series 2004, as provided in Section 9.02 of the
Series 2004 Trust Indenture.




In case of certain
events of default specified in the Indenture, the principal of this bond may be
declared or may become due and payable in the manner and with the effect
provided in the Indenture. No recourse shall be had for the payment of the
principal of or interest on this bond, or for any claim based hereon, or
otherwise in respect hereof or of the Indenture or any indenture supplemental
thereto, to or against any incorporator, stockholder, officer or director, past,
present or future, of the Company, or of any predecessor or successor
corporation, either directly or through the Company, or such predecessor or
successor corporation, under any constitution or statute or rule of law, or by
the enforcement of any assessment, penalty, or otherwise, all such liability of
incorporators, stockholders, directors and officers being waived and released by
the Registered Owner hereof by the acceptance of this bond and being likewise
waived and released by the terms of the Indenture.




This bond shall not
be assignable or transferable except as permitted or required by
Section 13.15 of the Series 2004 Trust Indenture. This bond is
exchangeable by the Registered Owner hereof, in person or by attorney duly
authorized, at the principal office or place of business of the Trustee under
the Indenture, upon the surrender and cancellation of this bond and the payment
of any stamp tax or other governmental charge, and upon any such exchange a new
registered bond or bonds without coupons, of the same series and maturity and
for the same aggregate principal amount, will be issued in exchange heretofore; *provided,* that the Company
shall not be required to exchange any bonds of Environmental Improvement
Series 2004 for a period of ten (10) days next preceding an Interest
Payment Date with respect to such bonds.




As provided in
Section 8.02 of the Series 2004 Trust Indenture, from and after the
Release Date (as defined in the Series 2004 Trust Indenture), the
obligations of the Company with respect to this bond shall be deemed to be
satisfied and discharged, this bond shall cease to secure in any manner any
Revenue Refunding Bonds Series 2004 outstanding under the Series 2004
Trust Indenture, and, pursuant to Section 8.02 of the Series 2004
Trust Indenture, the Trust Indenture Trustee shall forthwith deliver this bond
to the Company for cancellation.




This bond shall not
be valid or become obligatory for any purpose unless and until it shall have
been authenticated by the execution by the Trustee or its successor in trust
under the Indenture of the Trustee’s Certificate endorsed hereon.




In Witness
Whereof , Central Illinois
Public Service Company has caused this bond to be executed in its name by the
manual or facsimile signature of its President or one of its Vice-Presidents,
and its corporate seal or a facsimile thereof to be affixed or imprinted hereon
and attested by the manual or facsimile signature of its Secretary or one of its
Assistant Secretaries.




Central Illinois
Public Service Company




By
______________________________


President




Attest:




By_____________________________


Secretary




This bond is one of
the bonds of the series designated therein, described in the within mentioned
Indenture.




U.S. Bank National
Association, as
Trustee




By_______________________________


Authorized
Officer




**[END OF
FORM OF BOND]**




Now,
Therefore , in consideration
of the premises and of the sum of One Dollar ($1.00) duly paid by the Trustees
to the Company, and of other good and valuable considerations, the receipt
whereof is hereby acknowledged, and for the purpose of further assuring to the
Trustees under the Indenture their title to, or lien upon, the property
hereinafter described, under and








pursuant to
the terms of the Indenture, as hereby amended, and for the purpose of further
securing the due and punctual payment of the principal of and interest and the
premium, if any, on all bonds which have been heretofore or shall be hereafter
issued under the Indenture and indentures supplemental thereto and which shall
be at any time outstanding thereunder and secured thereby and $35,000,000
aggregate principal amount of the Environmental Improvement Series 2004,
and for the purpose of securing the faithful performance and observance of all
the covenants and conditions set forth in the Indenture and/or in any indenture
supplemental thereto, the Company has given, granted, bargained, sold,
transferred, assigned, pledged, mortgaged, warranted the title to and conveyed,
and by these presents does give, grant, bargain, sell, transfer, assign, pledge,
mortgage, warrant the title to and convey unto U.S. Bank National
Association and Patrick J.
Crowley , as Trustees under
the Indenture as therein provided, and their successors in the trusts thereby
created, and to their assigns, all the right, title and interest of the Company
in and to any and all premises, plants, property, leases and leaseholds,
franchises, permits, rights and powers, of every kind and description, real and
personal, which have been acquired by the Company through construction,
purchase, consolidation or merger, or otherwise, subsequent to March 31,
2001, and which are owned by the Company at the date of the execution hereof,
together with the rents, issues, products and profits therefrom, excepting,
however, and there is hereby expressly reserved and excluded from the lien and
effect of the Indenture and of this supplemental indenture, all right, title and
interest of the Company, now owned, in and to (a) all cash, bonds, shares
of stock, obligations and other securities not deposited with the Trustee or
Trustees under the Indenture, and (b) all accounts and bills receivable,
judgments (other than for the recovery of real property or establishing a lien
or charge thereon or right therein) and chooses in action not specifically
assigned to and pledged with the Trustee or Trustees under the Indenture, and
(c) all personal property acquired or manufactured by the Company for sale,
lease, rental or consumption in the ordinary course of business, and
(d) the last day of each of the demised terms created by any lease of
property leased to the Company and under each and every renewal of any such
lease, the last day of each and every such demised term being hereby expressly
reserved to and by the Company, and (e) all gas, oil and other minerals now
or hereafter existing upon, within or under any real estate of the Company
subject to, or hereby subjected to, the lien of the Indenture.




Without in any way
limiting or restricting the generality of the foregoing description or the
foregoing exceptions and reservations, the Company hereby expressly gives,
grants, bargains, sells, transfers, assigns, pledges, mortgages, warrants the
title to and conveys unto said U.S. Bank National
Association and Patrick J.
Crowley , as Trustees under
the Indenture, and unto their successor or successors in trust, and their
assigns, under the trusts and for the purposes of the Indenture, as hereby
amended, the properties described in Schedule A to this supplemental indenture,
which is incorporated herein by reference with the same force and effect as if
set forth at length herein, and which properties have been acquired by the
Company, through construction, purchase, consolidation or merger, or otherwise,
subsequent to March 31, 2001 (except as otherwise indicated in said
Schedule A), and which are owned by the Company at the date of the execution
hereof together with the tenements, hereditaments and appurtenances thereunto
belonging or appertaining, to have and to hold all
said property, rights and interests forever, but in trust,
nevertheless , upon the trusts,
for the purposes and subject to all the terms, conditions, provisions and
restrictions of the Indenture, as hereby amended.







And upon the
considerations and for the purposes aforesaid, and in order to provide, pursuant
to the terms of the Indenture, for the issuance under the Indenture, as hereby
amended, of bonds of Environmental Improvement Series 2004 and to fix the
terms, provisions and characteristics of the bonds of Environmental Improvement
Series 2004, and to modify or amend the Indenture in the particulars and to
the extent hereinafter in this supplemental indenture specifically provided, the
Company hereby covenants and agrees with the Trustees as follows:




**Article
I**




*Section 1.1* . A
series of bonds issuable under the Indenture, as hereby amended, to be known and
designated as “First Mortgage Bonds, Environmental Improvement Series 2004”
and which shall be executed, authenticated and issued only in the form of
registered bonds without coupons, is hereby created and authorized. The bonds of
Environmental Improvement Series 2004 and the Trustee’s Certificate to be
endorsed thereon shall be substantially in the form thereof hereinbefore
recited. Each bond of Environmental Improvement Series 2004 is to be issued
and registered in the name of UMB Bank, N.A., as trustee, or a successor trustee
(said trustee or any successor trustee being hereinafter referred to as the *“Trust
Indenture Trustee”* ), under the
Indenture of Trust dated as of October 1, 2004 between the Illinois Finance
Authority (the *“Authority”* ) and the Trust
Indenture Trustee (the *“Series 2004
Trust Indenture”* ), to secure any
and all obligations of the Company under the Series 2004 Loan Agreement
relating to the Revenue Refunding Bond Series 2004. Each bond of Environmental
Improvement Series 2004 shall be dated as of the Interest Payment Date thereof
to which interest was paid next preceding the date of issue, unless
(a) issued on an Interest Payment Date thereof to which interest was paid,
in which event it shall be dated as of such issue date, or (b) issued prior
to the occurrence of the first Interest Payment Date thereof to which interest
was paid, in which event it shall be dated the Original Issue Date specified in
the form of bond. The bonds of Environmental Improvement Series 2004 shall be
due and payable in the principal amount and on the Maturity Date specified
below, subject to prior redemption, shall bear interest from the date thereof at
the interest rate or rates (as determined in accordance with the Series 2004
Trust Indenture referred to above), but in no event shall the interest rate
exceed eighteen percent (18%) per annum payable, on the Interest Payment Dates
as determined in accordance with the Series 2004 Trust Indenture referred to in
the form of bond to the Registered Owner as specified on the registry books of
the Trustee at the close of business of the Trustee on the applicable Record
Date as provided in Section 3 of this Article I.


Series
    Maturity
      Date
    Principal
      Amount
    Interest
      Rate2004
    July 1,
      2025
    $35,000,000
    *




The bonds of
Environmental Improvement Series 2004 shall be payable, as to both principal and
interest, in immediately available funds, at the office or agency of the Trust
Indenture Trustee, in any coin or currency of the United States of America which
at the time of payment is legal tender for public and private debts.






As determined in accordance with the Series 2004 Trust
Indenture.








*Section*  *1.2* . 
A nything contained
in Section 14 of Article I of the Indenture, or elsewhere in the
Indenture, to the contrary notwithstanding, only the person in whose name any of
the bonds of Environmental Improvement Series 2004 is registered (the *“Registered
Owner”* ) at the close of
business on any Record Date, as hereinafter defined, with respect to any
Interest Payment Date shall be entitled to receive the interest payable on such
Interest Payment Date notwithstanding the cancellation of such bonds upon any
transfer or exchange subsequent to the Record Date and prior to such Interest
Payment Date; *provided,
however,* that if and to the
extent the Company shall default in the payment of the interest due on such
Interest Payment Date, such defaulted interest shall be paid to the persons in
whose names outstanding bonds of Environmental Improvement Series 2004 are
registered on the Record Date to be established by the Trustee for payment of
such defaulted interest.




Upon any payment of
the principal of, premium, if any, and interest on, all or any portion of the
Revenue Refunding Bonds Series 2004, whether at maturity or prior to maturity by
redemption or otherwise or upon provision for the payment thereof having been
made in accordance with Section 8.01 of the Series 2004 Trust Indenture,
bonds of Environmental Improvement Series 2004 in a principal amount equal to
the principal amount of such Revenue Refunding Bonds Series 2004 and having both
a corresponding maturity date and interest rate shall, to the extent of such
payment of principal, premium, if any, and interest, be deemed paid and the
obligation of the Company thereunder to make such payment shall be discharged to
such extent and, in the case of the payment of principal (and premium, if any),
such bonds of Environmental Improvement Series 2004 shall be surrendered to the
Trustee for delivery to the Company for cancellation as provided in
Section 8.02 of the Series 2004 Trust Indenture. The Trustee may at anytime
and all times conclusively assume that the obligation of the Company to make
payments with respect to the principal of and premium, if any, and interest on
the Revenue Refunding Bonds Series 2004, so far as such payments at the time
have become due, has been fully satisfied and discharged pursuant to the
foregoing sentence unless and until the Trustee shall have received a written
notice from the Trust Indenture Trustee signed by one of its officers stating
(i) the timely payment of principal, or premium or interest on, the Revenue
Refunding Bonds Series 2004 has not been made, (ii) that the Company is in
arrears as to the payments required to be made by it to the Trust Indenture
Trustee pursuant to the Series 2004 Trust Indenture, and (iii) the amount
of the arrearage.




*Section 1.3* . The
term “Record Date” as used herein with respect to any Interest Payment Date
(other than an Interest Payment Date for the payment of defaulted interest)
shall mean the applicable Record Date, next preceding such Interest Payment
Date, as determined in accordance with the Series 2004 Trust Indenture
referred to in the form of bond, or, if such Record Date shall be a legal
holiday or a day on which banking institutions in the City of Chicago, Illinois,
are authorized by law to close, then the next preceding day which shall not be a
legal holiday or a day on which such institutions are so authorized to
close.




*Section
1.4* . The
bonds of Environmental Improvement Series 2004 are not redeemable except on
the respective dates, in the respective principal amounts and for the respective
redemption prices that correspond to the redemption dates for, the principal
amounts to be redeemed of, and the redemption prices for, the Revenue Refunding
Bonds Series 2004, and except as set forth in Section 1.5
hereof.







In the event that
the Company redeems any Revenue Refunding Bonds Series 2004 bonds prior to
maturity in accordance with the provisions of the Series 2004 Trust
Indenture, the Trust Indenture Trustee shall on the same date deliver to the
Company the bonds of Environmental Improvement Series 2004 in principal
amounts corresponding to the Revenue Refunding Bonds Series 2004 so
redeemed, as provided in Section 8.02 of the Series 2004 Trust
Indenture. The Company agrees to give the Trust Indenture Trustee notice of any
such redemption of the Revenue Refunding Bonds Series 2004 on or before the
date fixed for any such redemption.




*Section
1.5* . Upon
the occurrence of an Event of Default under the Series 2004 Trust Indenture
and the acceleration of the Revenue Refunding Bonds Series 2004, the bonds
of Environmental Improvement Series 2004 shall be redeemable in whole upon
receipt by the Trustee of a written demand (hereinafter called a *“Redemption
Demand”* ) from the Trust
Indenture Trustee stating that there has occurred under the Series 2004
Trust Indenture both an Event of Default and a declaration of acceleration of
payment of principal, accrued interest and premium, if any, on the Revenue
Refunding Bonds Series 2004 specifying the last date to which interest on
such Revenue Refunding Bonds Series 2004 has been paid (such date being
hereinafter referred to as the *“Initial
Interest Accrual Date”* ) and demanding
redemption of the bonds of Environmental Improvement Series 2004. The
Company waives any right it may have to prior notice of such redemption under
the Indenture. Upon surrender of the bonds of Environmental Improvement
Series 2004 by the Trust Indenture Trustee to the Trustee, the bonds of
Environmental Improvement Series 2004 shall be redeemed at a redemption
price equal to the principal amount thereof plus accrued interest thereon from
the Initial Interest Accrual Date to the date of the Redemption Demand; *provided,
however,* that in the event
of a rescission or annulment of acceleration of Revenue Refunding Bonds
Series 2004 pursuant to Section 9.02(b) of the Series 2004 Trust
Indenture, then any Redemption Demand shall thereby deemed to be rescinded by
the Trust Indenture Trustee although no such rescission or annulment shall
extend to or affect any subsequent default or impair any right consequent
thereon.




*Section 1.6.* The bonds of
Environmental Improvement Series 2004 shall not be assignable or
transferable except as permitted by Section 13.15 of the Series 2004
Trust Indenture. Any such transfer shall be effected at the principal office or
place of business of the Trustee under the Indenture. The bonds of Environmental
Improvement Series 2004 are exchangeable by the Registered Owner thereof,
in person or by attorney duly authorized, at the principal office or place of
business of the Trustee under the Indenture, upon the surrender and cancellation
of said bonds and the payment of any stamp tax or other governmental charge, and
upon any such exchange a new registered bond or bonds without coupons, of the
same series and maturity and for the same aggregate principal amount, will be
the same series and maturity and for the same aggregate principal amount, will
be issued in exchange theretofore; and *provided,* that the Company
shall not be required to exchange any bonds of Environmental Improvement
Series 2004 for a period of ten (10) days next preceding an Interest
Payment Date with respect to bonds of Environmental Improvement
Series 2004.




The bonds of
Environmental Improvement Series 2004 shall, from time to time, be executed
on behalf of the Company and sealed with the corporate seal of the Company, all
in the manner provided or permitted by Section 6 of Article I of the
Indenture, as follows:







(a) bonds
of Environmental Improvement Series 2004 executed on behalf of the Company
by its President or a Vice-President and/or by its


Secretary or an
Assistant Secretary may be so executed by the facsimile signature of such
President or Vice-President and/or of such Secretary or Assistant Secretary, as
the case may be, of the Company, or of any person or persons who shall have been
such officer or officers, as the case may be, of the Company on or subsequent to
the date of this supplemental indenture, notwithstanding that he or they may
have ceased to be such officer or officers of the Company at the time of the
actual execution, authentication, issue or delivery of any of such bonds, and
any such facsimile signature or signatures of any such officer or officers on
any such bonds shall constitute execution of such bonds on behalf of the Company
by such officer or officers of the Company for the purposes of the Indenture, as
hereby amended, and shall be valid and effective for all purposes, *provided* that all bonds
shall always be executed on behalf of the Company by the signature, manual or
facsimile, of its President or a Vice-President and of its Secretary or an
Assistant Secretary, and *provided,
further,* that none of such
bonds shall be executed on behalf of the Company by the same officer or person
acting in more than one capacity; and




(b) such
corporate seal of the Company may be a facsimile, and any bonds of Environmental
Improvement Series 2004 on which such facsimile


seal shall be
affixed, impressed, imprinted or reproduced shall be deemed to be sealed with
the corporate seal of the Company for the purposes of the Indenture, as hereby
amended, and such facsimile seal shall be valid and effective for all
purposes.




*Section
1.7* . As provided in
Section 8.02 of the Series 2004 Trust Indenture, from and after the
Release Date (as defined in the Series 2004 Trust Indenture), the
obligations of the Company with respect to the bonds of Environmental
Improvement Series 2004 shall be deemed to be satisfied and discharged, the
bonds of Environmental Improvement Series 2004 shall cease to secure in any
manner any bonds of Revenue Refunding Bonds Series 2004 outstanding under
the Series 2004 Trust Indenture, and, pursuant to Section 8.02 of the
Series 2004 Trust Indenture, the Trust Indenture Trustee shall forthwith
deliver the bonds of Environmental Improvement Series 2004 to the Company
for cancellation.




**Article
II**




*Section 2.1* . Sections 10 and 16
of Article III of the Indenture are, and each of them is, hereby amended by
striking out the words “Series X through Series Z, Series 1995-1,
Series 1997-1, Series 1997-2, Senior Notes Series AA-1, Senior
Notes Series AA-2 and Senior Notes Series BB” wherever the same occur
in each of said sections, and by inserting, in lieu thereof, the words
“Series 1995-1, Series 1997-2, Senior Notes Series AA-1, Senior
Notes Series AA-2, Senior Notes Series BB and Environmental
Improvement Series 2004” and the Company hereby covenants and agrees to
observe and comply with the provisions of said sections as hereby
amended.







**Article
III**




*Section
3.1* . The
provisions of this supplemental indenture shall become and be effective from and
after the execution hereof, and the Indenture, as hereby amended, shall remain
in full force and effect.




*Section
3.2* . Each reference in
the Indenture, or in this supplemental indenture, to any article, section, term
or provision of the Indenture shall mean and be deemed to refer to such article,
section, term or provision of the Indenture, as hereby amended, except where the
context otherwise indicates.




*Section
3.3.* All the covenants,
provisions, stipulations and agreements in this supplemental indenture contained
are and shall be for the sole and exclusive benefit of the parties hereto, their
successors and assigns, and of the holders and Registered Owners from time to
time of the bonds of Environmental Improvement Series 2004 and of the
coupons issued and outstanding from time to time under and secured by the
Indenture, as hereby amended, and the Trust Indenture Trustee, for the benefit
of the holder or holders of the Revenue Refunding Bonds
Series 2004.




This supplemental
indenture has been executed in a number of identical counterparts, each of which
so executed shall be deemed to be an original.




At the time of the
execution of this supplemental indenture, the aggregate principal amount of all
indebtedness of the Company outstanding, or to be presently outstanding, under
and secured by the Indenture, as hereby amended, is $340,000,000, evidenced by
First Mortgage Bonds of the series listed below, issued by the Company under
said Indenture and now outstanding or to be presently issued by it under said
Indenture, as follows:





PrincipalSeries
    Interest
      Rate (%)
    Maturity
      Date
    Amount($)1995-1
    6.49
    June
      1, 2005
    20,000,0001997-2
    7.05
    June
      1, 2006
    20,000,0001997-2
    7.61
    June
      1, 2017
    40,000,000Senior
      Notes AA-1
    5.375
    December
      15, 2008Senior
      Notes AA-2
    6.125%
    December
      15, 2028
    60,000,000Senior
      Notes BB
    6.625%
    June
      15, 2011
    150,000,000Series
      2004
    *
    July
      1, 2025
    35,000,000(a)Total........
    
    340,000,000


*    As determined in
accordance with the Series 2004 Trust Indenture.


(a) To be
presently issued by the Company under said Indenture.












In Witness
Whereof , said Central
Illinois Public Service Company has caused this instrument to be executed in its
corporate name by its President or a Vice President and its corporate seal or a
facsimile thereof to be hereunto affixed and to be attested by its Secretary or
an Assistant Secretary, and said U.S. Bank National Association, for the purpose
of entering into and joining with the Company in the execution of this
supplemental indenture, has caused this instrument to be executed in its
corporate name by one of its Vice Presidents and its corporate seal to be
hereunto affixed and to be attested by one of its Assistant Vice Presidents, and
said Patrick J. Crowley, for the purpose of entering into and joining with the
Company in the execution of this supplemental indenture, has signed and sealed
this instrument; all as of the day and year first above written.







Central Illinois
Public Service Company




By: /s/ Jerre E.
Birdsong


Jerre E.
Birdsong


Vice President and
Treasurer


(Corporate
Seal)




Attest:




By /s/ G.L.
Waters


G.L.
Waters


Assistant
Secretary




U.S. Bank National
Association




By: /s/ James P.
Vellanti


James P.
Vellanti


Vice
President


(Corporate
Seal)




Attest:




By /s/ Cheryl L.
Clarke


Cheryl L.
Clarke


Assistant Vice
President


/s/
Patrick J.
Crowley (SEAL)


Patrick
J. Crowley













State of
Missouri          )


)  SS


City of
St. Louis          
)




I, Carolyn J.
Shannon, a Notary Public, do hereby certify that Jerre E. Birdsong, Vice
President and Treasurer of Central Illinois
Public Service Company , a corporation
organized and existing under the laws of the State of Illinois, and G.L. Waters,
Assistant Secretary of said corporation, who are both personally known to me to
be the same persons whose names are subscribed to the foregoing instrument as
such officers, respectively, of said corporation, and who are both personally
known to me to be such officers, appeared before me this day in person and
severally acknowledged that they signed, sealed and delivered said instrument as
their free and voluntary act as such officers, and as the free and voluntary act
of said corporation, for the uses and purposes therein set forth.




Given under my hand
and official seal this 9 th day of November,
2004, in the City and State aforesaid.








/s/ Carolyn J.
Shannon


Notary
Public





( Notarial
Seal )



















State of New
York            
)


) SS


County of New
York         )




I, Patricia V.
Cowart, a Notary Public in and for New York County in the State aforesaid, do
hereby certify that:




James P.
Vellanti, a Vice President of U.S. Bank National
Association , a national
banking association, and Stacey A. Pagliaro, an Assistant Vice President of
said association, who are both personally known to me to be the same persons
whose names are subscribed to the foregoing instrument as such officers,
respectively, of said association, and who are both personally known to me to be
such officers, appeared before me this day in person and severally acknowledged
that they signed, sealed and delivered said instrument as their free and
voluntary act as such officers, and as the free and voluntary act of said
association, for the uses and purposes therein set forth.




Given under my hand
and official seal this 10th day of November, 2004.








/s/ Patricia V.
Cowart


Patricia V.
Cowart


Notary
Public


( Notarial
Seal )


















State of New
York            
)


) SS


County of New
York         )







I, Sima Glater, a
Notary Public in and for New York County in the State aforesaid, do hereby
certify that:




Patrick J. Crowley,
personally known to me to be the same person whose name is subscribed to the
foregoing instrument, appeared before me this day in person and acknowledged
that he signed, sealed and delivered said instrument as his free and voluntary
act, for the uses and purposes therein set forth.




Given under my hand
and official seal this 10th day of November, 2004.








/s/ Sima
Glater


Sima
Glater


Notary
Public


( Notarial
Seal )























**Schedule
A**




To the Supplemental
Indenture dated October 1, 2004




of Central Illinois
Public Service Company to




U.S. Bank National
Association and




Patrick J. Crowley
as trustees




The properties of
the Company acquired through construction, purchase, consolidation or merger or
otherwise subsequent to March 31, 2001 and prior to June 1, 2004 referred to in
the foregoing Supplemental Indenture, located in the counties of Adams, Brown,
Calhoun, Champaign, Christian, Clay, Coles, Edgar, Effingham, Fulton, Jasper,
Mason, McDonough, Menard, Sangamon, and Williamson in the State of Illinois as
described as follows:




First . The following
described electric substation of the Company located in, or in the vicinity of,
the following community located in the State of Illinois:





LocationCommunity
    
    County
    
    KVAFlora
    
    Clay
    
    5,250







Second . The following
described gas distribution mains of the Company located in the State of
Illinois, as follows:


LOCATION
    APPROXIMATE
      LENGTH IN
      FEETCOMMUNITY
    COUNTYMarion
    Williamson
    13,569Breeds
    Fulton
    21,527Smithfield
    Fulton
    2,973Hardin
    Calhoun
    3,870Quincy
    Adams
    16,651Havana
    Mason
    11,907Macomb
    McDonough
    3,437New
      Berlin
    Sangamon
    3,016Forest
      City
    Mason
    26,767Petersburg
    Menard
    3,659Athens
    Menard
    4,265Mattoon
    Coles
    7,540Paris
    Edgar
    5,540Kincaid
    Christian
    3,451Effingham
    Effingham
    9,737Mt
      Sterling
    Brown
    2,700Newton
    Jasper
    5,020Cantrall-
      Andrew
    Sangamon
    6,056




Third . The following
described real estate situated in Clay County, Illinois (Property Index Number:
13-01-100-015; Common Street Address: No address has been
assigned.):




A part of Lot One
(1) of the Northeast Quarter (NE1⁄4) of the NW Quarter (NW1⁄4) of Section One (1),
Township Two North (T2N), Range Five East (R5E) of the 3 rd Principal
Meridian, Clay County, Illinois, more particularly described as
follows:




Commencing at the
Southwest Corner of said Lot 1 of the NE 1⁄4 of the NW 1⁄4 of said Section 1, thence
N 1° 24’ 37” E, 388.31 feet along the West line of Lot 1 to the Point of
Beginning. Thence N 89° 55’ 55” E, 145.31 feet; Thence N 1° 24’ 37” E, 214.64
feet to a point on the centerline of Vincennes & St. Louis Road (Route
250); Thence S 76° 58’ 10” W, 150.00 feet along the centerline of Vincennes
& St. Louis Road (Route 250) to a point on the West line of Lot 1; Thence S
1° 24’ 37” W, 180.98 feet to the Point of Beginning, containing 0.66 acres, more
or less.




Fourth . The following
described real estate situated in Champaign County, Illinois (Property Index
Number: 29-26-26-458-009; Common Street Address: No address has been
assigned.):




Part of the
Southeast Quarter of Section 26, Township 18 North, Range 8 East of the Third
Principal Meridian, Village of Tolono, Champaign County, Illinois, more
particularly described as follows: Commencing at an iron pipe survey monument
found at the Southeast corner of the Southeast Quarter of Section 26, Township
18 North, Range 8 East of the Third Principal Meridian, Champaign County,
Illinois; thence North 89° 22’ 23” West along the South line of the Southeast
Quarter of said Section 26, a distance of 1,758.87 feet to an iron pipe survey
monument reset on the existing Westerly right of way line of the Canadian
National/Illinois Central Railroad for the point of beginning; thence North 89°
22’ 23” West along the South line of said Section 26, a distance of 175.54 feet
to an iron pipe survey monument reset on the former Westerly right of way line
of the Illinois Central Railroad; thence North 06° 50’ 58” East along the former
Westerly right of way line of the Illinois Central Railroad, a distance of
342.40 feet to an iron pipe survey monument found at the Southwesterly corner of
the State of Illinois tract as filed of record as Case Number 95-L-31 in the
Office of the Circuit Clerk of Champaign County, Illinois; thence South 46° 51’
19” East along the Southerly line of said State of Illinois Tract, a distance of
191.69 feet to an iron pipe survey monument found; thence South 83° 09’ 02” East
along the Southerly line of said State of Illinois tract, a distance of 20.00
feet to an iron pipe survey monument found on said existing Westerly right of
way line of the Canadian National/Illinois Central Railroad; thence South 06°
50’ 58” West along said existing Westerly right of way line of the Canadian
National/Illinois Central Railroad, a distance of 209.91 feet to the point of
beginning, containing 1.08 acres more or less.




Fifth . The following
described real estate situated in Fulton County, Illinois (Property Index
Numbers: 09-08-28-408-13 and 09-08-28-408-014; Common Street Addresses: No
addresses have been assigned.):




Tract
A




A part of the
Southeast Quarter of Section 28, Township 7 North, Range 4 East of the Fourth
Principal Meridian, Fulton County, Illinois, more particularly described as
follows and bearings are for descriptive purposes only:




Commencing at the
Northeast corner of the Southeast Quarter of Section 28, thence along the east
line of said Section 28 bearing South 00 degrees 34 minutes 38 seconds West, a
distance of 844.77 feet to the projection of the south right-of-way line of
Illinois State Route 9, thence along said projection and said south right-of-way
line bearing South 89 degrees 50 minutes 53 seconds West, a distance of 347.29
feet to the Point of Beginning of the parcel to be described:




From said Point of
Beginning, thence bearing South 00 degrees 13 minutes 43 seconds East, a
distance of 176.53 feet to the north line of Homewood Addition Block 2; thence
along said north line bearing South 89 degrees 24 minutes 34 seconds West, a
distance of 183.91 feet to the southwest corner of the City of Canton Property;
thence along the westerly line of said City of Canton Property bearing North 00
degrees 32 minutes 26 seconds East, a distance of 36.96 feet; thence continuing
along said westerly line bearing North 29 degrees 39 minutes 06 seconds East, a
distance of 162.57 feet to said south right-of-way line; thence along said south
right-of-way line bearing North 89 degrees 50 minutes 53 seconds East, a
distance of 102.42 feet; to the Point of Beginning, containing 0.615 acres more
or less.




Tract
B




A part of the
Southeast Quarter of Section 28, Township 7 North, Range 4 East of the Fourth
Principal Meridian, Fulton County, Illinois, more particularly described as
follows and bearings are for descriptive purposes only:




Commencing at the
Northeast corner of the Southeast Quarter of Section 28, thence along the east
line of said Section 28 bearing South 00 degrees 34 minutes 38 seconds West, a
distance of 844.77 feet to the projection of the south right-of-way line of
Illinois State Route 9, thence along said projection and said south right-of-way
line bearing South 89 degrees 50 minutes 53 seconds West, a distance of 449.71
feet; thence along said south right-of-way line bearing South 29 degrees 39
minutes 06 seconds West, a distance of 28.81 feet to the northeast corner of the
Hicksgas Canton, Inc., property and the Point of Beginning of the parcel to be
described.




From said Point of
Beginning, thence along the East line of said Hicksgas Canton, Inc., property
bearing South 29 degrees 39 minutes 06 seconds West, a distance of 107.79 feet
to the southeast corner of said Hicksgas Canton, Inc., property; thence along
the south line of said Hicksgas Canton, Inc., property bearing South 89 degrees
50 minutes 53 seconds West, a distance of 142.91 feet; thence bearing North 38
degrees 49 minutes 30 seconds East, a distance of 152.48 feet to said south
right-of-way line; thence along said south right-of-way line of the next three
courses bearing North 89 degrees 50 minutes 53 seconds East, a distance of 28.08
feet; thence bearing South 00 degrees 09 minutes 07 seconds East, a distance of
25.00 feet; thence bearing North 89 degrees 50 minutes 53 seconds East, a
distance of 72.50 feet to the Point of Beginning, containing 0.305 acres more or
less.




*Permanent
Restriction* . No improvements
shall be constructed upon the premises conveyed within 50 feet of the liquid
propane storage tanks now located or to be located upon Grantor’s premises
unless Grantor, its successors or assigns, has given written permission to
Grantee, its successors or assigns, to construct a particular
improvement.