Upper Stewartsville is an unincorporated community and census-designated place (CDP) located within Greenwich Township in Warren County, in the U.S. state of New Jersey, that was defined as part of the 2010 United States Census.

[12] According to the United States Census Bureau, the CDP had a total area of 0.070 square miles (0.182 km2), all of which was land.

[1][2] The 2010 United States census counted 212 people, 76 households, and 58 families in the CDP.

There were 84 housing units at an average density of 1,192.1 per square mile (460.3/km2).

Of all households, 19.7% were made up of individuals and 9.2% had someone living alone who was 65 years of age or older.