Seaside Park is a borough in Ocean County, in the U.S. state of New Jersey. It is part of the New Brunswick–Lakewood, NJ Metropolitan Division, which is part of the New York metropolitan area. As of the 2020 United States census, the borough's population was 1,436, a decrease of 143 (−9.1%) from the 2010 census count of 1,579, which in turn had reflected decline of 684 (−30.2%) from the 2,263 counted in the 2000 census. Seaside Park is situated on the Barnegat Peninsula, a long, narrow barrier peninsula that separates Barnegat Bay from the Atlantic Ocean.

The Barnegat Peninsula, also known as the Island Beach Peninsula or Barnegat Bay Island and colloquially as "the barrier island", is a 20-mile (32 km) long, narrow barrier peninsula located on the Jersey Shore in Ocean County, New Jersey, United States, that divides the Barnegat Bay from the Atlantic Ocean. It is a vacation destination and summer colony area and is heavily dependent on tourism, real estate and fishing.