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is a city in Boone County, Illinois, United States. The population was 20,820 at the 2000 census. It is the county seat of Boone County. 2005 population estimates show a large increase, as the population rose to 24,593.
Belvidere is located at (42.254758, -88.844093), and sits at an altitude that is approximately above sea level. Located in north central Illinois, Belvidere is approximately northwest of the downtown of Chicago, and approximately east of Rockford. Belvidere is divided by the Kishwaukee River.
According to the United States Census Bureau, the city has a total area of 9.1 square miles (23.6 km²), of which, 9.1 square miles (23.5 km²) of it is land and 0.1 square miles (0.1 km²) of it (0.55%) is water.