Belvidere, IL -- U.S. city in Illinois Population (2000): 20820 Housing Units (2000): 7970 Land area (2000): 9.070897 sq. miles (23.493515 sq. km) Water area (2000): 0.052795 sq. miles (0.136738 sq. km) Total area (2000): 9.123692 sq. miles (23.630253 sq. km) FIPS code: 05092 Located within: Illinois (IL), FIPS 17 Location: 42.254758 N, 88.844093 W ZIP Codes (1990): 61008 Note: some ZIP codes may be omitted esp. for suburbs. Headwords: Belvidere, IL Belvidere