Janesville, IA -- U.S. city in Iowa Population (2000): 829 Housing Units (2000): 359 Land area (2000): 1.448151 sq. miles (3.750695 sq. km) Water area (2000): 0.044942 sq. miles (0.116398 sq. km) Total area (2000): 1.493093 sq. miles (3.867093 sq. km) FIPS code: 39405 Located within: Iowa (IA), FIPS 19 Location: 42.646008 N, 92.462663 W ZIP Codes (1990): 50647 Note: some ZIP codes may be omitted esp. for suburbs. Headwords: Janesville, IA Janesville