Belvidere is a town in Warren County, New Jersey, United States. As of the 2010 United States Census, the town's population was 2,681, reflecting a decline of 90 (-3.2%) from the 2,771 counted in the 2000 Census, which had in turn increased by 102 (+3.8%) from the 2,669 counted in the 1990 Census. It is the county seat of Warren County.