Butler County is a county located in the southwestern part of the U.S. state of Ohio. As of the 2020 census, the population was 390,357. Its county seat is Hamilton. It is named for General Richard Butler, who died in 1791 during St. Clair's Defeat. Located along the Great Miami River, it is also home to Miami University, a public university founded in 1809.Butler County is part of the Cincinnati, OH-KY-IN Metropolitan Statistical Area. The majority of the county is in District 52 of the State House.