Mountain Lake is an unincorporated community and census-designated place (CDP)[9] located within Liberty Township in Warren County, in the U.S. state of New Jersey,[10] that was created as part of the 2010 United States Census.

[1][2] The 2010 United States census counted 575 people, 261 households, and 154 families in the CDP.

There were 315 housing units at an average density of 278.7 per square mile (107.6/km2).

The racial makeup was 95.65% (550) White, 0.52% (3) Black or African American, 0.17% (1) Native American, 1.39% (8) Asian, 0.00% (0) Pacific Islander, 0.87% (5) from other races, and 1.39% (8) from two or more races.

Of all households, 32.2% were made up of individuals and 11.1% had someone living alone who was 65 years of age or older.