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 and largest city 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.

Hamilton is a city in and the county seat of Butler County, Ohio, United States. Located 20 miles (32 km) north of Cincinnati, Hamilton is the second-largest city in the Greater Cincinnati area and the tenth-largest city in Ohio. The population was 63,399 at the 2020 census. Most of the city is served by the Hamilton City School District.