Blairstown is an unincorporated community and census-designated place (CDP) located within Blairstown Township, in Warren County, in the U.S. state of New Jersey. The CDP was created as part of the 2010 United States census. As of the 2010 United States census, the CDP's population was 515.

According to the United States Census Bureau, the CDP had a total area of 0.432 square miles (1.120 km), including 0.425 square miles (1.102 km) of land and 0.007 square miles (0.019 km) of water (1.65%).

Historical population

Census	Pop.	Note	%±
2010	515		—
2020	493		−4.3%
U.S. Decennial Census 2010 2020

The 2010 United States census counted 515 people, 201 households, and 134 families in the CDP. The population density was 1,210.7 per square mile (467.5/km). There were 219 housing units at an average density of 514.8 per square mile (198.8/km). The racial makeup was 96.89% (499) White, 0.78% (4) Black or African American, 0.00% (0) Native American, 0.58% (3) Asian, 0.00% (0) Pacific Islander, 0.97% (5) from other races, and 0.78% (4) from two or more races. Hispanic or Latino of any race were 3.50% (18) of the population.

Of the 201 households, 30.3% had children under the age of 18; 41.8% were married couples living together; 17.4% had a female householder with no husband present and 33.3% were non-families. Of all households, 26.4% were made up of individuals and 5.5% had someone living alone who was 65 years of age or older. The average household size was 2.42 and the average family size was 2.93.

22.7% of the population were under the age of 18, 10.7% from 18 to 24, 25.8% from 25 to 44, 32.6% from 45 to 64, and 8.2% who were 65 years of age or older. The median age was 37.6 years. For every 100 females, the population had 114.6 males. For every 100 females ages 18 and older there were 109.5 males.