Belvidere is a Town in Warren County, New Jersey, United States. As of the United States 2000 Census, the town population was 2,771. It is the county seat of Warren County. Belvidere was incorporated as a town by an Act of the New Jersey Legislature on April 7, 1845, from portions of Oxford Township, based on the results of a referendum held that day. Belvidere is located in the eastern section of the Lehigh Valley.