Charleroi ( /ʃɔːlərɔɪ/ shaw-lə-roy) is a borough in Washington County, Pennsylvania, along the Monongahela River, 25 miles south of Pittsburgh. Charleroi was settled in 1890 and incorporated in 1891. The population in 1900 stood at 5,930; in 1910, 9,615; in 1920, 11,516, and in 1940, 10,784. The population was 4,871 at the 2000 census.
There has been a large-scale cessation of industrial activities in the region. The decrease in the population is associated with the decline of the steel-making industry in the "Mon Valley" which extends from Charleroi to the mouth of the Monongahela at Pittsburgh.
Charleroi is a namesake and Sister city of Charleroi, Belgium. The name is French for "Charles [the] King" (referring to King Charles II of Spain). Charleroi was home to one of the first movie theatres in the nation, the electric theatre which opened in October 1905. The Pittsburgh Plate Glass Company, today PPG Industries, had one of its major factories located at the current chamber plaza, at one point employing up to a thousand employees, making it one of the largest glass factories in the world at the time. For years it was the home to one of Corning Glass Companies leading employers. Today it is home to World Kitchen, which makes pyrex, giving it the distinction of being the only plant in the United States to make it.