Stanhope is a borough in Sussex County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 3,526, a decrease of 84 from the 2010 census count of 3,610, which in turn reflected an increase of 26 from the 3,584 counted in the 2000 census. Stanhope was formed by an act of the New Jersey Legislature on March 24, 1904, from portions of Byram Township.