​CHARLEROI, a borough of Washington county, Pennsylvania, U.S.A., on the Monongahela river, near the S.W. corner of the state, about 20 m. S. of Pittsburgh. Pop. (1900) 5930, (1749 foreign-born); (1910) 9615. It is served by the Pennsylvania railway. The surrounding country has good farming land and large coal mines. In 1905 the borough ranked fifth among the cities of the United States in the manufacture of glass (plate-glass, lamp chimneys and bottles), its product (valued at $1,841,308) being 2.3% of that of the whole country. Charleroi was settled in 1890 and was incorporated in 1891.