Hazlet is a township in Monmouth County, in the U.S. state of New Jersey. The township is located near the Raritan Bay within the Raritan Valley region. It is located in the New York Metropolitan Area and is a bedroom community of New York City. As of the 2020 United States census, the township's population was 20,125, a decrease of 209 (−1.0%) from the 2010 census count of 20,334, which in turn reflected a decline of 1,044 (−4.9%) from the 21,378 counted in the 2000 census.