A spokesman for the FBI's Cleveland division said Tuesday he couldn't comment on what prompted the searches because the federal search warrants were sealed. Agent Scott Wilson also wouldn't say whether anyone was taken into custody.
He says one restaurant is in Evansville, Ind., and the others are in the Toledo area.
The Blade newspaper in Toledo reported officials carried away boxes of documents.
Wilson says the searches involved the FBI, the Internal Revenue Service and Homeland Security investigations through U.S. Immigration and Customs Enforcement.
A spokesman for IHOP's parent company, DineEquity, told the Evansville Courier and Press the company is cooperating and was told the investigation does not involve terrorism.