Monessen is a city in Westmoreland County, Pennsylvania, United States. The population was 7,720 at the 2010 census. In 1940, 20,257 people lived there. In 1990 the population was 13,026. Steel-making was a prominent industry in Monessen, which was a Rust Belt borough in the "Mon Valley" of southwestern Pennsylvania that became a third-class city in 1921. It is near Charleroi and Donora, two similar places with similar histories. According to the United States Census Bureau, the city has a total area of 3.1 square miles (8.0 km2), of which, 2.9 square miles (7.5 km2) of it is land and 0.2 square miles (0.52 km2) of it (4.90%) is water.
- Douglas Education Center is a private, for profit higher education career school, located in Monessen.
- Monessen City School District is a public school district in Westmoreland County, Pennsylvania.