Mountain Lake, New Jersey

Mountain Lake is an unincorporated community and census-designated place (CDP) located within Liberty Township in Warren County, in the U.S. state of New Jersey, that was created as part of the 2010 United States Census. As of the 2020 United States census, the CDP's population was 494 a decrease of 81 (−14.1%) from the 575 recorded at the 2010 census.

Geography
According to the United States Census Bureau, the CDP had a total area of 1.305 square miles (3.381 km2), including 1.130 square miles (2.927 km2) of land and 0.175 square miles (0.453 km2) of water (13.41%).

2010 census
The 2010 United States census counted 575 people, 261 households, and 154 families in the CDP. The population density was 508.7 /sqmi. There were 315 housing units at an average density of 278.7 /sqmi. 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. Hispanic or Latino of any race were 2.43% (14) of the population.

Of the 261 households, 23.0% had children under the age of 18; 44.8% were married couples living together; 8.8% had a female householder with no husband present and 41.0% were non-families. 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. The average household size was 2.20 and the average family size was 2.84.

17.7% of the population were under the age of 18, 9.0% from 18 to 24, 22.1% from 25 to 44, 38.1% from 45 to 64, and 13.0% who were 65 years of age or older. The median age was 45.3 years. For every 100 females, the population had 99.7 males. For every 100 females ages 18 and older there were 98.7 males.