Highland Park is a borough in Middlesex County, in the U.S. state of New Jersey, in the New York City metropolitan area. The borough is located on the northern banks of the Raritan River, in the Raritan Valley region. As of the 2020 United States census, the borough's population was 15,072, an increase of 1,090 (+7.8%) from the 2010 census count of 13,982, which in turn reflected a decline of 17 (−0.1%) from the 13,999 counted in the 2000 census.

The Raritan River is a major river of New Jersey. Its watershed drains much of the mountainous area of the central part of the state, emptying into the Raritan Bay on the Atlantic Ocean.