Monessen is a city in southwestern Westmoreland County, Pennsylvania, United States, located along the Monongahela River.

With restructuring of the steel industry in the later 20th century and loss of jobs, it is considered a Rust Belt borough in the "Mon Valley" of southwestern Pennsylvania.

Named for the Monongahela River and the industrial German city of Essen, Monessen was created by land speculators fairly late in the history of the Mon Valley, after neighboring towns had already been settled.

James M. Schoonmaker, who made his fortune in coke, owned a controlling interest in the land company.

[4] In May 1897, National Tin Plate Company, founded by William Donner, began building its mill, thus becoming Monessen's first employer.

[5] Monessen experienced rapid growth in the first two decades of the 20th century; the population increasing from 2,197 in 1900 to 11,775 in 1910 and then to 18,179 in 1920.

[5] Beginning in the middle to late 1960s, the region's manufacturers, especially the steel industry, found it harder to compete, which led to employee layoffs.

In 1972, the closure of Page Steel and Wire Company was a major setback to the city.

In January 2010 the first female mayor, Mary Jo Smith, was sworn in at the Monessen Municipal Building.

Younger residents barely remember the mills or are even unaware of the city's industrial past.

[9] Monessen is rich in it’s Military Veterans who fought in WW1, WW11 Korea, Vietnam and the Gulf wars.

The climate in this area is characterized by hot, humid summers and generally mild to cool winters.

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).