 Across the Monongahela River in Washington County, Monessen runs adjacent to Carroll and Fallowfield Townships and North Charleroi (with a direct connector via Charleroi-Monessen Bridge).As of the census of 2000, there were 8,669 people, 3,916 households, and 2,451 families residing in the city.The population density was 2,986.8 people per square mile (1,154.2/km2).