Seaside Heights is a borough in Ocean County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 2,887, reflecting a decline of 268 (-8.5%) from the 3,155 counted in the 2000 Census, which had in turn increased by 789 (+33.3%) from the 2,366 counted in the 1990 Census. Seaside Heights is situated on the Barnegat Peninsula, a long, narrow barrier peninsula that separates Barnegat Bay from the Atlantic Ocean.