Charleroi (/ˈʃɑːrlərɔɪ/ SHAR-lə-roy) is a borough in Washington County, Pennsylvania, United States, along the Monongahela River, 21 miles south of Pittsburgh.

Colloquially, the stretch from Charleroi north to McKeesport (historically because of press coverage of High School sports leagues), is known as the "Mon Valley," and has been extended by some to mean from the river mouth to northern West Virginia.

Once dubbed "Magic City," Charleroi has in recent years seen a gradual revitalization of its business district.

Many Belgian immigrants lived in the Monongahela area at the end of the 19th century, some of whom were glass makers.

[7][8] The Pittsburgh Plate Glass Company, now 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.

[10][11] In 2020, Paul Magnette, mayor of Charleroi (Belgium) visited the town that was founded by migrants from his city.

Across the Monongahela River to the east, Charleroi runs adjacent with Rostraver Township in Westmoreland County.

By 2024, the borough received immigrants from various countries including Haiti, Jamaica, and Liberia.