Union Township is a township in Washington County, Pennsylvania, United States. The population was 5,700 at the 2010 census.HistoryThe Dusmal House and Mingo Creek Presbyterian Church and Churchyard are listed on the National Register of Historic Places.GeographyAccording to the United States Census Bureau, the township has a total area of 15.7 square miles (40.8 km²), of which, 15.4 square miles (39.8 km²) of it is land and 0.4 square miles (1.0 km²) of it (2.41%) is water.DemographicsAs of the census of 2000, there were 5,599 people, 2,300 households, and 1,674 families residing in the township. The population density was 364.3 people per square mile (140.6/km²). There were 2,376 housing units at an average density of 154.6/sq mi (59.7/km²). The racial makeup of the township was 98.25% White, 0.68% African American, 0.04% Native American, 0.16% Asian, 0.23% from other races, and 0.64% from two or more races. Hispanic or Latino of any race were 0.54% of the population.