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 from the 2010 census count of 841, which in turn reflected a decline of 4 from the 845 counted in the 2000 census. The borough is located in the northernmost region of Sussex County. Branchville was incorporated as a borough by an act of the New Jersey Legislature on March 9, 1898, from portions of Frankford Township.