Lake Hopatcong is a census-designated place (CDP)[5] in Jefferson Township, Morris County, New Jersey, United States.

It includes communities on the northeast side of Lake Hopatcong, the largest freshwater body in the state.

[2] The Lake Hopatcong CDP occupies the southwest end of Jefferson Township in western Morris County.

It is partially bordered to the south by the borough of Mount Arlington and slightly by the Lower Berkshire Valley CDP.

About 77 acres (31 ha) of the island was bought by Richmond Boy Scout Council Executive Major Walter S. Stewart and Charles McAteer in 1922.