Fairfield, city, Butler County, southwestern Ohio, on the Great Miami River, near Cincinnati; incorporated 1955. It is chiefly residential. Manufactures include automobile parts, industrial fans, doors, electronic equipment, chemicals, and plastic products. A junior college is here. The city, settled around 1800, is named for local topographic features. Population 30,777 (1980); 39,729 (1990); 42,097 (2000).
