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                                                                     EXHIBIT 5.1

                  EFFECTIVE DATE OF THE REGISTRATION STATEMENT

Firstar Corporation
777 East Wisconsin Avenue
Milwaukee, Wisconsin 53202

Ladies and Gentlemen:

     I am Senior Vice President, General Counsel and Secretary of Firstar
Corporation (the "Corporation") and, as such, I have acted as counsel for the
Corporation in the preparation of a Registration Statement on Form S-3 (the
"Registration Statement") to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, as amended, (the "Securities Act")
in connection with the proposed offer and sale of the following securities (the
"Securities") of the Corporation having an aggregate initial public offering
price of up to $1,000,000,000: (i) senior debt securities (the "Senior Debt
Securities"), (ii) subordinated debt securities (the "Subordinated Debt
Securities," and together with the Senior Debt Securities, the "Debt
Securities"), (iii) preferred stock and preference stock, par value $1.00 per
share (the "Preferred Stock"), of the Corporation, interests in which may be
evidenced by appropriately prepared depositary shares (the "Depositary Shares"),
(iv) common stock, par value $.01 per share, (the "Common Stock") of the
Corporation issuable upon conversion of Debt Securities, Preferred Stock, or
Depositary Shares, or upon exercise of warrants, and (v) appropriately prepared
warrants to purchase Debt Securities, Preferred Stock, or Common Stock
(collectively, the "Warrants"). The Securities may be offered separately or as
part of units with other Securities, in separate series, in amounts, at prices,
and on terms to be set forth in the prospectus and one or more supplements to
the prospectus (collectively, the "Prospectus") constituting a part of the
Registration Statement, and in the Registration Statement.

     The Senior Debt Securities are to be issued under an indenture in the form
filed as Exhibit 4.1 to the Registration Statement, with appropriate insertions,
(the "Senior Indenture") to be entered into by the Corporation and a trustee or
trustees to be named by the Corporation. The Subordinated Debt Securities are to
be issued under an indenture in the form filed as Exhibit 4.5 to the
Registration Statement, with appropriate insertions, (the "Subordinated
Indenture") to be entered into by the Corporation and a trustee or trustees to
be named by the Corporation. The Depositary Shares are to be issued under a
deposit agreement in the form filed as Exhibit 4.13 to the Registration
Statement, with appropriate insertions, (the "Deposit Agreement") to be entered
into by the Corporation, a depositary to be named by the Corporation, and the
holders from time to time of depositary receipts evidencing Depositary Shares.
The Common Stock and the Preferred Stock are to be issued under the Certificate
of Incorporation. The Warrants are to be issued under warrant agreements in the
forms filed as Exhibits 4.15 to 4.18 to the Registration Statement, with
appropriate insertions, (the "Warrant Agreements") to be entered into by the
Corporation and warrant agents to be named by the Corporation.

     Certain terms of the Securities to be issued by the Corporation from time
to time will be approved by the Board of Directors of the Corporation or a
committee thereof or certain authorized officers of the Corporation as part of
the corporate action taken and to be taken (the "Corporate Proceedings") in
connection with issuance of the Securities. I have examined or am otherwise
familiar with the Certificate of Incorporation, the By-Laws of the Corporation,
as amended, the Registration Statement, such of the Corporation Proceedings as
have occurred as of the date hereof, and such other documents, records, and
instruments as I have deemed necessary or appropriate for the purpose of this
opinion.

     Based on the foregoing, I am of the opinion that: (i) upon the execution
and delivery by the Corporation of the Senior Indenture or the Subordinated
Indenture, as the case may be, and the execution and delivery of the Deposit
Agreement, and the applicable Warrant Agreement, the completion of all required
Corporate Proceedings, and the execution, issuance, and delivery, and the
authentication by a duly appointed authenticating agent, of the Senior Debt
Securities and Subordinated Debt Securities, the Depositary Shares, and the
Warrants, respectively, pursuant to such agreements, such Senior Indenture,
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Subordinated Indenture, Deposit Agreement, or Warrant Agreement, as the case may
be, will become valid and binding instruments, and any Debt Securities issuable
thereunder will be legal, valid, and binding obligations of the Corporation
except in each case as enforcement of provisions of such instruments and
agreements may be limited by bankruptcy or other laws of general application
affecting the enforcement of creditors' rights and by general equity principles,
and any Depositary Shares, Warrants, or Preferred Stock (assuming completion of
the actions referred to in clause (ii) below) or Common Stock (assuming
completion of the actions referred to in clause (iii) below) issuable thereunder
will be duly and validly authorized and issued, fully paid, and nonassessable;
(ii) upon the authorization of issuance of the Preferred Stock, completion of
all required Corporate Proceedings and the execution, issuance, and delivery of
the Preferred Stock pursuant to such Certificate of Designations, the Preferred
Stock will be duly and validly authorized and issued, fully paid, and
nonassessable; and (iii) upon the authorization and issuance of the Common
Stock, the completion of all required Corporate Proceedings, and the execution,
issuance, and delivery of the Common Stock, the Common Stock will be duly and
validly authorized and issued, fully paid, and nonassessable. The foregoing
opinion assumes that (i) the consideration designated in the applicable
Corporate Proceedings for any Preferred Stock or Common Stock shall have been
received by the Corporation in accordance with applicable law; (ii) the Senior
Indenture, the Subordinated Indenture, the Deposit Agreement, and any Warrant
Agreement shall have been duly authorized, executed, and delivered by all
parties thereto other than the Corporation; (iii) the Registration Statement
shall have become effective under the Securities Act, and (iv) the applicable
Senior Indenture or Subordinated Indenture shall have become duly qualified
under the Trust Indenture Act of 1939, as amended.

     I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to being named in the Prospectus included therein
under the caption "Validity of Securities" with respect to the matters stated
herein.

                                          Very truly yours,

                                          /s/ JENNIE P. CARLSON
                                          --------------------------------------
                                          Jennie P. Carlson