Keansburg is a borough in Monmouth County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 10,105, which represented a decline of 627 from the 10,732 counted in the 2000 Census, which had in turn declined by 337 from the 11,069 counted in the 1990 Census.Keansburg was formed as a borough by an act of the New Jersey Legislature on March 26, 1917, from portions of both Middletown Township and Raritan Township, based on the results of a referendum held on April 17, 1917.The borough is part of the Bayshore Regional Strategic Plan, an effort by nine municipalities in northern Monmouth County to reinvigorate the area's economy by emphasizing the traditional downtowns, dense residential neighborhoods, maritime history, and the natural beauty of the Raritan Bay coastline.