- Located in the center of the Cincinnati/Dayton Metroplex, the City of Hamilton, founded in 1791, is the County Seat of Butler County, Ohio. The largest city in Butler County, with a population of approximately 65, 000 people, Hamilton is the center for government, finance, and industry. City Quick Phone Reference General Topic Phone Listing PRESIDENT BUSH VISITS HAMILTON PRESIDENT SIGNS LANDMARK ...www.hamilton-city.org