POWER OF ATTORNEY WITH RESPECT TO FORMS 3, 4 and 5

The undersigned hereby constitutes and appoints each of (i) the Secretary

and any Assistant Secretary of Northern Trust Corporation, and

(ii) Robert J. Regan, Paul A. Bernacki, Carlen Sellers,

Linda Morgan, and Karen Harris, of Schiff Hardin LLP, or any of the

foregoing persons acting singly, and with full power of substitution,

as the undersigned's true and lawful attorney-in-fact to:

(1) execute for and on behalf of the undersigned, in the

undersigned's capacity as an officer and/or director of

Northern Trust Corporation, a Delaware Corporation (the "Corporation"),

Forms 3, 4, and 5 in accordance with Section 16(a)

of the Securities Exchange Act of 1934 and the rules thereunder;

(2) do and perform any and all acts for and on behalf of the

undersigned that may be necessary or desirable to complete and

execute any such Form 3, 4, or 5, complete and execute any

amendment thereto, and file such Form with the United States Securities

and Exchange Commission, through the use of EDGAR, the

Electronic Data Gathering, Analysis,

and Retrieval system, and with any stock exchange or similar authority;

and

(3) take any other action of any type whatsoever in connection

with the foregoing which, in the opinion of such attorney-in-fact,

may be of benefit to, in the best interest of, or legally required

by, the undersigned, it being understood that the documents executed

by such attorney-in-fact on behalf of the undersigned pursuant to

this Power of Attorney shall be in such form and shall contain such

terms and conditions as such attorney-in-fact may approve in such

attorney-in-fact's discretion.

The undersigned hereby grants to each such attorney-in-fact full

power and authority to do and perform

any and every act and thing whatsoever requisite, necessary,

or proper to be done in the exercise of any of the rights and powers

herein granted, as fully to all intents and purposes as the undersigned

might or could do if personally present, with full power of

substitution or revocation, hereby ratifying and confirming all that such

attorney-in-fact, or such attorney-in-fact's substitute or substitutes,

shall lawfully do or cause to be done by virtue of this Power of Attorney

and the rights and powers herein granted.  The undersigned acknowledges

that the foregoing attorneys-in-fact, in serving in such capacity

at the request of the undersigned, are not assuming, nor is the

Corporation assuming, any of the undersigned's responsibilities to

comply with Section 16 of the Securities Exchange Act of 1934.

This Power of Attorney shall remain in full force and effect until

the undersigned is no longer required to file Forms 3, 4, and 5 with

respect to the undersigned's holdings of and transactions in

securities issued by the Corporation, unless earlier revoked by the

undersigned in a signed writing delivered to the foregoing

attorneys-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney

to be executed as of this 11th day of April 2007.

    /s/Joyce St. Clair



Power of Attorney-SEC Filings-2007

Section 16 POA.doc