Monessen is a city in Westmoreland County, Pennsylvania, United States. The population was 8,669 at the 2000 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.
Monessen, named for the Monongahela River and the German city of Essen, was created by land speculators fairly late in the history of the Mon Valley, after neighboring towns had already been settled. The East Side Land Company bought land from various farmers, laid out the streets, and then sold the lots to prospective residents and employers. James M. Schoonmaker, who had made his fortune in coke, owned a controlling interest in the land company. Other investors in the land company who were also immortalized in street names include Philander C. Knox, James H. Reed, H. Sellers McKee, George O. Morgan, and George B. Motheral. In May 1897, National Tin Plate Company, founded by William Donner, began building its mill, thus becoming Monessen’s first employer. Sales of lots began on July 27, 1897, for the general public and other employers. Monessen became a borough on September 3, 1898.
Monessen experienced rapid growth in the first two decades of the twentieth century, the population increasing from 2,197 in 1900 to 11,775 in 1910 and then to 18,179 in 1920.