Mount Oliver is a borough in Allegheny County, Pennsylvania, United States. The population was 3,394 at the 2020 census. It is a largely residential area situated atop a crest about 3 miles (5 km) west of the Monongahela River. The borough is surrounded entirely by the city of Pittsburgh, having resisted annexation attempts by the city.

John Ormsby (1720–1805) was a soldier in the French and Indian War, Pontiac's Rebellion, and the American Revolution, and among the first settlers of Pittsburgh, Pennsylvania. The son of the Anglo-Irish landed gentry, he emigrated from Ireland to the Thirteen Colonies in 1752. After Pontiac's Rebellion, he received a land grant from King George III, and established a homestead on the banks of the Monongahela River. He established extensive economic and merchant interests in Bedford, Pennsylvania, and at the head of the Ohio River.