Mount Oliver, PA

At the 2020 census, Mount Oliver was an Allegheny County borough of 3,394 people perched on a crest south of Pittsburgh. John Ormsby received 249 acres along the Monongahela in 1769, and the settlement later took his son Oliver's name. Residents began selling lots in 1800; when Lower St. Clair failed to give the hilltop much attention, 650 property owners signed a new incorporation petition in 1892. The original borough boundaries still mostly follow Ormsby's tract.

Mount Oliver is surrounded by Pittsburgh but has spent more than a century refusing to become part of it. When Pittsburgh tried to force annexation in 1927, the borough argued that its population gave residents the right to decide, and the city backed off. Brownsville Road runs along the crest as the main commercial spine, while Pittsburgh Public Schools serve Arlington School and Carrick High School. Two neighborhood parks and an old street grid fill out the present-day picture. Mount Oliver is a tiny independent municipality with a very large answer to the question of where Pittsburgh ends.