From Ohio History Central
On March 24, 1803, the State of Ohio established Butler County. The county was named in honor of Richard Butler, who was killed in St. Clair's defeat in 1791. It was originally part of Hamilton County.
Butler County is located in Ohio's southwestern corner. Its western boundary lies on the Indiana border. The county is generally rural, although urban areas cover twelve percent of Butler County's 467 square miles. The county's largest city is Hamilton, the county seat, with a population of 60,690 people in 2000. Middletown and Fairfield are the next two largest cities, with populations of more than forty thousand people in 2000. Almost 333,000 people resided in Butler County in 2000. This was an increase of more than fourteen percent since 1990. The county averages approximately 713 people per square mile.