Fairfield is a city in southern Butler County, Ohio, United States. It is a suburb located about 25 miles 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.