Highland Park is a borough in Middlesex County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 13,982, reflecting a decline of 17 from the 13,999 counted in the 2000 Census, which had in turn increased by 720 from the 13,279 counted in the 1990 Census.Highland Park was formed as a borough by an act of the New Jersey Legislature on March 15, 1905, when it broke away from what was then known as Raritan Township. The borough was named for its location above the Raritan River.