Fairfield is a city in southern Butler County, Ohio, United States. It is a suburb located about 25 miles (40 km) north of Cincinnati and is situated on the east bank of the Great Miami River. The population was 44,907 as of the 2020 census. Incorporated in 1955 from portions of Fairfield Township, it includes the former hamlets of Symmes Corner, Fair Play, Furmandale, and Stockton. The Fairfield City School District is one of the largest in Ohio and serves both the City of Fairfield and Fairfield Township.

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.