Coraopolis is a borough in Allegheny County, Pennsylvania, USA. The population was 6,131 at the 2000 census. In 1940 the population peaked at 11,086. It is a small community located to the west of Pittsburgh, along the Ohio River. The borough is noted for its steep topography, numerous brick streets and many large, old and exquisite homes. The American Bridge Company is headquartered in Coraopolis.