First Midwest Bancorp (ONBPP) S-8 Registration of securities for employees

Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the Registration Statement (Form S-8 No. 333-00000) pertaining to the Omnibus Stock and Incentive Plan of First Midwest Bancorp, Inc. of our reports dated February 27, 2009, with respect to the consolidated financial statements of First Midwest Bancorp, Inc. and the effectiveness of internal control over financial reporting of First Midwest Bancorp, Inc. included in its Annual Report (Form 10-K) for the year ended December 31, 2008, filed with the Securities and Exchange Commission.

Ernst & Young LLP

Chicago, Illinois

May 21, 2009