Hopatcong is a Borough in Sussex County, New Jersey, United States. As of the United States 2000 Census, the borough population was 15,888. The area had been called "Brookland" in the 1800s and the lake that was expanded to become Lake Hopatcong had been known as "Great Pond" or "Brookland Pond". During the 1803s, the name of the community had been modified to "Brooklyn", to match the spelling of the city on New York's Long Island. Hopatcong was originally established as the Town of Brooklyn on April 2, 1898 from portions of Byram Township. On March 22, 1901, the Borough of Hopatcong replaced Brooklyn. In 1922, residents of Byram Cove, Northwood, and other areas to the west of the original land area of the borough, voted to leave Byram Township and join Hopatcong, leaving the Borough with its current borders.