Phillipsburg is a town in Warren County, New Jersey, United States, a sister city to the cross-Delaware River industrial partner of Easton, Pennsylvania.The town is located along the Delaware River in western New Jersey, on the border with Pennsylvania, and is considered part of the Delaware Valley region and the eastern border of the Lehigh Valley region. The Norfolk Southern Railway's Lehigh Line, runs through Phillipsburg on its way cross river to Easton, Pennsylvania. The Belvidere Delaware Railroad was leased and later acquired by the Pennsylvania Railroad connecting the lower Poconos to Trenton, New Jersey and Philadelphia.As of 2010 United States Census, the town's population was 14,950, reflecting a decline of 216 from the 15,166 counted in the 2000 Census, which had in turn declined by 591 from the 15,757 counted in the 1990 Census.