Andover is a borough in Sussex County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 595, a decrease of 11 (−1.8%) from the 2010 census count of 606, which in turn reflected a decline of 52 (−7.9%) from the 658 counted in the 2000 census.

Andover Township is a township in Sussex County, in the U.S. state of New Jersey. As of the 2020 United States census, the township's population was 5,996, a decrease of 323 (−5.1%) from the 2010 census count of 6,319, which in turn reflected an increase of 286 (+4.7%) from the 6,033 counted in the 2000 census.