Branchville 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 791, a decrease of 50 (−5.9%) from the 2010 census count of 841, which in turn reflected a decline of 4 (−0.5%) from the 845 counted in the 2000 census. The borough is located in the northernmost region of Sussex County.