Lake Hopatcong is a census-designated place (CDP) 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. As of the 2020 United States census, the population was 10,232.

The Lake Hopatcong CDP occupies the southwest end of Jefferson Township in western Morris County. It is bordered to the west by the borough of Hopatcong and to the north by Sparta Township, both in Sussex County. It is partially bordered to the south by the borough of Mount Arlington and slightly by the Lower Berkshire Valley CDP.

Lake Hopatcong, the water body, occupies part of the western boundary of the CDP, while the northernmost arm of the lake is entirely within the CDP. Lakefront communities in the CDP include Espanong, Prospect Point, Raccoon Island, and Woodport, and inland communities include Hurdtown, Tierneys Corner, and Berkshire Valley. Lake Shawnee is in the northeast part of the CDP. New Jersey Route 15 passes through the eastern side of the CDP, leading south 4 miles (6 km) to Interstate 80 in Wharton and north 6 miles (10 km) to Sparta.

According to the U.S. Census Bureau, the Lake Hopatcong CDP has a total area of 9.39 square miles (24.32 km), of which 7.39 square miles (19.14 km) are land and 2.00 square miles (5.18 km), or 21.34%, are water. The lake, with an outlet 2 miles (3 km) to the southwest into the Musconetcong River, is part of the Delaware River watershed.

The community was first listed as a CDP prior to the 2020 census.

Historical population

Census	Pop.	Note	%±
2020	10,232		—
U.S. Decennial Census 2020

People who were born in, residents of, or otherwise closely associated with Lake Hopatcong include:

• Tim Jacobus (born 1959), artist best known for illustrating the covers for nearly one hundred books in R. L. Stine's Goosebumps series
• Jaren Sina (born 1994), professional basketball player, who played for Astoria Bydgoszcz of the Polish Basketball League