Andover is a borough in Sussex County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 606, reflecting a decline of 52 (-7.9%) from the 658 counted in the 2000 Census, which had in turn declined by 42 (-6.0%) from the 700 counted in the 1990 Census.
Andover was incorporated as a borough by an act of the New Jersey Legislature on March 25, 1904, from portions of Andover Township. The borough was named for Andover Township, which was in turn named for Andover, Hampshire, England.
According to the United States Census Bureau, the borough had a total area of 1.36 square miles (3.53 km2), including 1.35 square miles (3.49 km2) of land and 0.02 square miles (0.04 km2) of water (1.18%).
The borough borders the Sussex County municipalities of Andover Township, Byram Township and Green Township.
The 2010 United States Census counted 606 people, 241 households, and 164 families in the borough. The population density was 417.3 inhabitants per square mile (161.1/km2). There were 263 housing units at an average density of 181.1 per square mile (69.9/km2). The racial makeup was 91.75% (556) White, 1.16% (7) Black or African American, 0.33% (2) Native American, 2.15% (13) Asian, 0.00% (0) Pacific Islander, 2.64% (16) from other races, and 1.98% (12) from two or more races. Hispanic or Latino of any race were 7.59% (46) of the population.
Of the 241 households, 28.6% had children under the age of 18; 50.6% were married couples living together; 12.4% had a female householder with no husband present and 32.0% were non-families. Of all households, 22.8% were made up of individuals and 9.1% had someone living alone who was 65 years of age or older. The average household size was 2.51 and the average family size was 2.91.
21.1% of the population were under the age of 18, 7.6% from 18 to 24, 28.7% from 25 to 44, 30.5% from 45 to 64, and 12.0% who were 65 years of age or older. The median age was 40.4 years.