High Quality Content by WIKIPEDIA articles! Keansburg (pronounced "KEENS-burg") is a borough in Monmouth County, New Jersey, United States. As of the 2010 United States Census, the borough population was 10,105, which represented a decline of 627 (-5.8%) from the 10,732 counted in the 2000 Census, which had in turn declined by 337 (-3.0%) from the 11,069 counted in the 1990 Census.