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                                                                    Exhibit 4.12

                              DECLARATION OF TRUST
                                       OF
                           TRUSTMARK CAPITAL TRUST III


               THIS DECLARATION OF TRUST is made as of March 14, 2003 (this
"Declaration of Trust"), by and among Trustmark Corporation, as Depositor (the
"Depositor"), Wilmington Trust Company, as Delaware trustee (the "Delaware
Trustee"), Wilmington Trust Company, as property trustee (the "Property
Trustee"), and Richard Hickson, Zach Wasson, and T. Harris Collier III, as
trustees (the "Administrative Trustees"; and together with the Delaware Trustee
and the Property Trustee, the "Trustees"). The Depositor and the Trustees hereby
agree as follows:

               1. The trust created hereby shall be known as "Trustmark Capital
Trust III" (the "Trust"), in which name the Trustees or the Depositor, to the
extent provided herein, may conduct the business of the Trust, make and execute
contracts, and sue and be sued.

               2. The Depositor hereby assigns, transfers, conveys and sets over
to the Trustees the sum of $10. The Trustees hereby acknowledge receipt of such
amount in trust from the Depositor, which amount shall constitute the initial
trust estate. The Trustees hereby declare that they will hold the trust estate
in trust for the Depositor. It is the intention of the parties hereto that the
Trust created hereby constitute a statutory trust under Chapter 38 of Title 12
of the Delaware Code, 12 Del. C. ss. 3801, et seq. (the "Statutory Trust Act"),
and that this document constitute the governing instrument of the Trust. The
Trustees are hereby authorized and directed to execute and file a certificate of
trust with the Delaware Secretary of State in such form as the Trustees may
approve.

               3. The Depositor and the Trustees will enter into an amended and
restated Declaration of Trust satisfactory to each such party and substantially
in the form to be included as an exhibit to the Registration Statement on Form
S-3 (the "1933 Act Registration Statement") referred to below, or in such other
form as the Trustees and the Depositor may approve, to provide for the
contemplated operation of the Trust created hereby and the issuance of the
Preferred or Capital Securities and Common Securities referred to therein. Prior
to the execution and delivery of such amended and restated Declaration of Trust,
the Trustees shall not have any duties or obligations hereunder or with respect
of the trust estate, except as otherwise required by applicable law or as may be
necessary to obtain prior to such execution and delivery any licenses, consents
or approvals required by applicable law or otherwise. Notwithstanding the
foregoing, the Trustees may take all actions deemed proper as are necessary to
effect the transactions contemplated herein.

               4. The Depositor, as the sponsor of the Trust, is hereby
authorized (i) to file with the Securities and Exchange Commission (the
"Commission") and to execute, in the case of the 1933 Act Registration Statement
and 1934 Act Registration Statement (as herein defined), on behalf of the Trust,
(a) the 1933 Act Registration Statement, including pre-effective or
post-effective amendments to such Registration Statement, relating to the
registration under the

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Securities Act of 1933, as amended (the "1933 Act"), of the Preferred or Capital
Securities of the Trust, (b) any preliminary prospectus or prospectus supplement
thereto relating to the Preferred or Capital Securities required to be filed
under the 1933 Act, and (c) a Registration Statement on Form 8-A or other
appropriate form (the "1934 Act Registration Statement") (including all
pre-effective and post-effective amendments thereto) relating to the
registration of the Preferred or Capital Securities of the Trust under the
Securities Exchange Act of 1934, as amended; (ii) to file with the New York
Stock Exchange or other exchange, and execute on behalf of the Trust a listing
application and all other applications, statements, certificates, agreements and
other instruments as shall be necessary or desirable to cause the Preferred or
Capital Securities to be listed on the New York Stock Exchange or such other
exchange or quotation system; (iii) to file and execute on behalf of the Trust
such applications, reports, surety bonds, irrevocable consents, appointments of
attorney for service of process and other papers and documents as shall be
necessary or desirable to register the Preferred or Capital Securities under the
securities or "Blue Sky" laws of such jurisdictions as the Depositor, on behalf
of the Trust, may deem necessary or desirable; (iv) to execute and deliver
letters or documents to, or instruments for filing with, a depository relating
to the Preferred or Capital Securities; and (v) to execute, deliver and perform
on behalf of the Trust an underwriting agreement with the Depositor and the
underwriter or underwriters of the Capital Securities of the Trust. In the event
that any filing referred to in clauses (i)-(iii) above is required by the rules
and regulations of the Commission, the New York Stock Exchange or other exchange
or quotation system, or state securities or Blue Sky laws to be executed on
behalf of the Trust by a trustee, any Administrative Trustee, in his capacity as
a trustee of the Trust, is hereby authorized and directed to join in any such
filing and to execute on behalf of the Trust any and all of the foregoing, it
being understood that an Administrative Trustee, in his capacity as a trustee of
the Trust, shall not be required to join in any such filing or execute on behalf
of the Trust any such document unless required by the rules and regulations of
the Commission, the New York Stock Exchange or other exchange, or state
securities or Blue Sky laws. In connection with all of the foregoing, the
Trustees, solely in their capacities as trustees of the Trust, and the Depositor
hereby constitute and appoint Zach Wasson as the Depositor's true and lawful
attorney-in-fact and agent, with full power of substitution and resubstitution
for the Depositor or in the Depositor's name, place and stead, in any and all
capacities, to sign any and all amendments (including all pre-effective and
post-effective amendments) to the 1933 Act Registration Statement and the 1934
Act Registration Statement and to file the same, with all exhibits thereto, and
any other documents in connection therewith, with the Commission, granting unto
said attorney-in-fact and agent full power and authority to do and perform each
and every act and thing requisite and necessary to be done in connection
therewith, as fully to all intents and purposes as the Depositor might or could
do in person, hereby ratifying and confirming all that said attorney-in-fact and
agent or his respective substitute or substitutes, shall do or cause to be done
by virtue hereof.

               5. This Declaration of Trust may be executed in one or more
counterparts.

               6. The number of Trustees of the Trust initially shall be five
and thereafter the number of trustees of the Trust shall be such number as shall
be fixed from time to time by a written instrument signed by the Depositor which
may increase or decrease the number of Trustees of the Trust; provided, however,
that to the extent required by the Statutory Trust Act, one trustee of the Trust
shall either be a natural person who is a resident of the State of Delaware



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or, if not a natural person, an entity which has its principal place of business
in the State of Delaware. Subject to the foregoing, the Depositor is entitled to
appoint or remove without cause any trustee of the Trust at any time. Any
trustee of the Trust may resign upon thirty days' prior notice to the Depositor.

               7. The Depositor hereby agrees to (i) reimburse the Trustees for
all reasonable expenses (including reasonable fees and expenses of counsel and
other experts) and (ii) indemnify, defend and hold harmless the Trustees and any
of the officers, directors, employees and agents of the Trustees (the
"Indemnified Persons") from and against any and all losses, damages,
liabilities, claims, actions, suits, costs, expenses, disbursements (including
the reasonable fees and expenses of counsel), taxes and penalties of any kind
and nature whatsoever (collectively, "Expenses"), to the extent that such
Expenses arise out of or are imposed upon or asserted at any time against such
Indemnified Persons with respect to the performance of this Declaration of
Trust, the creation, operation or termination of the Trust or the transactions
contemplated hereby; provided, however, that the Depositor shall not be required
to indemnify any Indemnified Person for any Expenses which are a result of the
willful misconduct, bad faith or gross negligence of such Indemnified Person.

               8. This Declaration of Trust shall be governed by, and construed
in accordance with, the laws of the State of Delaware (with regard to conflict
of laws principles).





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               IN WITNESS WHEREOF, the parties hereto have caused this
Declaration of Trust to be duly executed as of the day and year first above
written.

                                TRUSTMARK CORPORATION,
                                as Depositor


                                By:   /s/ Richard Hickson
                                      ---------------------------------
                                      Name:  Richard Hickson
                                      Title:  Chairman, President and Chief
                                               Executive Officer



                                WILMINGTON TRUST COMPANY, as Delaware Trustee


                                By:   /s/ Mary St. Amand
                                      ---------------------------------
                                      Name:  Mary St. Amand
                                      Title: AVP


                                WILMINGTON TRUST COMPANY, as Property Trustee



                                By:   /s/ Mary St. Amand
                                      ---------------------------------
                                      Name:  Mary St. Amand
                                      Title: AVP


                                /s/ Richard Hickson
                                -------------------------------------
                                Richard Hickson, as Administrative Trustee

                                /s/ Zach Wasson
                                -------------------------------------
                                Zach Wasson, as Administrative Trustee

                                /s/ T. Harris Collier III
                                -------------------------------------
                                T. Harris Collier III, as Administrative Trustee