Branchville is a borough in Sussex County, New Jersey, in the United States. As of the United States 2000 Census, the borough population was 845. 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. An additional portion of Frankford Township was annexed as of March 1, 1951.