Exhibit 99(a)



PROXY

           THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS

                                       OF

                            CENTURY BANCSHARES, INC.

The undersigned hereby appoints Kim Culp and Kenneth D. Brooks proxies, each
with power to act without the other and with power of substitution, and hereby
authorizes them to represent and vote, as designated on the other side, all the
shares of stock of Century Bancshares, Inc. standing in the name of the
undersigned with all powers which the undersigned would possess if present at
the Special Meeting of Shareholders of Century Bancshares, Inc. to be held
February 26, 2002 or any adjournment or postponement thereof.

THIS PROXY, WHEN PROPERLY EXECUTED, WILL BE VOTED IN THE MANNER DIRECTED HEREIN
BY THE UNDERSIGNED SHAREHOLDER. IF NO DIRECTION IS MADE, THIS PROXY WILL BE
VOTED FOR PROPOSAL 1.

1.   Approval of the agreement and plan of merger dated December 3, 2001 by and
     between Marshall & Ilsley Corporation and Century Bancshares, Inc.,
     including the form of plan of merger constituting a part thereof, and the
     merger of Century Bancshares, Inc. with and into Marshall & Ilsley
     Corporation contemplated by that agreement.

         FOR      AGAINST      ABSTAIN

         [_}        [_]          [_]


2.   In their discretion, the Proxies are authorized to vote upon such other
     business as may properly come before the meeting and any adjournment or
     postponement thereof.

Please sign exactly as name appears hereon. When shares are held by joint
tenants, both should sign. When signing as attorney, executor, administrator,
trustee, or guardian, please give full title as such. If a corporation, please
sign in full corporate name by President or other authorized officer. If a
partnership, please sign in partnership name by authorized person.

Dated:_______________________________________, 2002


_____________________________________________
                  (Signature)


_____________________________________________
            (Signature if held jointly)


         PLEASE SIGN, DATE, AND RETURN THE PROXY CARD PROMPTLY USING THE
                               ENCLOSED ENVELOPE.




                            CENTURY BANCSHARES, INC.
                                 Special Meeting

                                       of

                      Century Bancshares, Inc. Shareholders
                           Tuesday, February 26, 2002
                                   10:00 a.m.
                            Century Bancshares, Inc.
                               11455 Viking Drive
                             Eden Prairie, Minnesota



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