Stewartsville is an unincorporated community and census-designated place (CDP) located within Greenwich Township in Warren County, New Jersey, United States, that was created as part of the 2010 United States Census. As of the 2010 Census, the CDP's population was 349. The area is served as United States Postal Service ZIP code 08886.
The Kennedy House and Mill, located on Route 173, is listed on the National Register of Historic Places (as Reference #: 96000552).
The community of Stewartsville was named after Thomas Stewart, a secretary to George Washington who purchased property in the area in 1793.
According to the United States Census Bureau, the CDP had a total area of 0.129 square miles (0.333 km2), all of which was land.
The 2010 United States Census counted 349 people, 134 households, and 96 families in the CDP. The population density was 2,714.4 inhabitants per square mile (1,048.0/km2). There were 144 housing units at an average density of 1,120.0 per square mile (432.4/km2). The racial makeup was 93.98% (328) White, 4.58% (16) Black or African American, 0.00% (0) Native American, 0.57% (2) Asian, 0.00% (0) Pacific Islander, 0.00% (0) from other races, and 0.86% (3) from two or more races. Hispanic or Latino of any race were 6.30% (22) of the population.
Of the 134 households, 36.6% had children under the age of 18; 52.2% were married couples living together; 14.2% had a female householder with no husband present and 28.4% were non-families. Of all households, 21.6% were made up of individuals and 8.2% had someone living alone who was 65 years of age or older. The average household size was 2.60 and the average family size was 3.05.
26.4% of the population were under the age of 18, 7.4% from 18 to 24, 26.4% from 25 to 44, 27.8% from 45 to 64, and 12.0% who were 65 years of age or older. The median age was 40.3 years. For every 100 females, the population had 97.2 males.