Lake Hopatcong is the largest freshwater body in the state of New Jersey, USA, approximately 4 square miles in area with lake front homes on all banks. The lake is located in the mountains of northern New Jersey, north of Netcong and along the border between Sussex and Morris county.
Lakefront homes are located within the borders of four municipalities, Hopatcong, Jefferson Township, Roxbury Township, and Mount Arlington. In the eighteenth century, the lake existed in two separate parts known as the "Great Pond" on the south and "Little Pond" on the north.
A natural body of water, the area of the lake has been enlarged by the damming of the Musconetcong River, its natural outlet, on the southern side of the lake.