Sussex is a borough in Sussex County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 2,130, reflecting a decline of 15 (-0.7%) from the 2,145 counted in the 2000 Census, which had in turn declined by 56 (-2.5%) from the 2,201 counted in the 1990 Census.
Sussex was incorporated as a borough by an act of the New Jersey Legislature on October 14, 1891, as Deckertown, from portions of Wantage. The borough was renamed Sussex on March 2, 1902.
A joint commission of residents of both Sussex and Wantage had recommended that the two communities should be consolidated to form what would be called the Township of Sussex-Wantage, which would operate under the Faulkner Act (Council-Manager) form of government with a mayor and a six-member township council, and that voters in both municipalities should approve a referendum to be held on November 3, 2009. The committee noted that the two municipalities share common issues, schools, library and community services and that the artificial nature of the octagonal Sussex border often made it hard to distinguish between the two. The efforts at consolidation with surrounding Wantage Township ended in November 2009 after Wantage voters rejected the merger despite support from Sussex borough residents.