EXHIBIT 23 CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM We hereby consent to the incorporation by reference in the Registration Statement on Form S-8 (Nos. 33-47074; 33-47147; 33-57557; 33-63101; 333-66129; 333-72787 and 333-78953) of FirstMerit Corporation of our report dated March 4, 2005 relating to the financial statements, management's assessment of the effectiveness of internal control over financial reporting and the effectiveness of internal control over financial reporting, which appears in this Form 10-K. /s/ PricewaterhouseCoopers LLP PricewaterhouseCoopers LLP Columbus, Ohio March 7, 2005