Green Knoll is an unincorporated community and census-designated place (CDP) located within Bridgewater Township, in Somerset County, in the U.S. state of New Jersey. As of the 2020 census, Green Knoll had a population of 6,594.
According to the United States Census Bureau, Green Knoll had a total area of 4.710 square miles (12.199 km<sup>2</sup>), including 4.707 square miles (12.191 km<sup>2</sup>) of land and 0.003 square miles (0.008 km<sup>2</sup>) of water (0.07%).
Green Knoll first appeared as a census designated place in the 2010 U.S. census.
The 2010 United States census counted 6,200 people, 2,441 households, and 1,628 families in the CDP. The population density was . There were 2,521 housing units at an average density of . The racial makeup was 79.60% (4,935) White, 3.21% (199) Black or African American, 0.13% (8) Native American, 14.82% (919) Asian, 0.00% (0) Pacific Islander, 0.79% (49) from other races, and 1.45% (90) from two or more races. Hispanic or Latino of any race were 6.08% (377) of the population.
Of the 2,441 households, 31.1% had children under the age of 18; 56.9% were married couples living together; 7.0% had a female householder with no husband present and 33.3% were non-families. Of all households, 30.1% were made up of individuals and 19.3% had someone living alone who was 65 years of age or older. The average household size was 2.46 and the average family size was 3.10.
22.5% of the population were under the age of 18, 5.5% from 18 to 24, 20.7% from 25 to 44, 29.2% from 45 to 64, and 22.0% who were 65 years of age or older. The median age was 45.7 years. For every 100 females, the population had 85.1 males. For every 100 females ages 18 and older there were 81.8 males.