Middletown, OH -- U.S. city in Ohio Population (2000): 51605 Housing Units (2000): 23144 Land area (2000): 25.656744 sq. miles (66.450660 sq. km) Water area (2000): 0.144364 sq. miles (0.373902 sq. km) Total area (2000): 25.801108 sq. miles (66.824562 sq. km) FIPS code: 49840 Located within: Ohio (OH), FIPS 39 Location: 39.506007 N, 84.375885 W ZIP Codes (1990): 45042 Note: some ZIP codes may be omitted esp. for suburbs. Headwords: Middletown, OH Middletown