Princeton Junction is an unincorporated community and census-designated place (CDP) located within West Windsor Township, in Mercer County, New Jersey, United States. As of the 2010 United States Census, the CDP's population was 2,465.
According to the United States Census Bureau, the CDP had a total area of 1.853 square miles (4.801 km2), including 1.826 square miles (4.730 km2) of land and 0.027 square miles (0.071 km2) of water (1.48%).
Princeton Junction's name comes from the train station of the same name, now on the Amtrak and New Jersey Transit Northeast Corridor. The station is the junction between this main line and a spur served by the "Dinky" train, run by New Jersey Transit, to Princeton itself.
The 2010 United States Census counted 2,465 people, 921 households, and 696.276 families in the CDP. The population density was 1,349.8 inhabitants per square mile (521.2/km2). There were 940 housing units at an average density of 514.7 per square mile (198.7/km2). The racial makeup was 74.81% (1,844) White, 2.43% (60) Black or African American, 0.16% (4) Native American, 18.62% (459) Asian, 0.00% (0) Pacific Islander, 1.42% (35) from other races, and 2.56% (63) from two or more races. Hispanic or Latino of any race were 5.44% (134) of the population.
Of the 921 households, 35.0% had children under the age of 18; 68.6% were married couples living together; 5.4% had a female householder with no husband present and 24.4% were non-families. Of all households, 20.8% were made up of individuals and 11.5% had someone living alone who was 65 years of age or older. The average household size was 2.66 and the average family size was 3.08.
25.0% of the population were under the age of 18, 4.6% from 18 to 24, 23.0% from 25 to 44, 30.6% from 45 to 64, and 16.8% who were 65 years of age or older. The median age was 43.3 years.