Plum is often referred to as "Plum Boro" or more correctly "Plum Borough" by locals to distinguish it from its previous status as a township. It was founded as Plum Township in 1788 and was reorganized as a borough in 1956. The borough took its name from nearby Plum Creek.
The 1889 history of Allegheny County, Pennsylvania, describes the township as having "no villages of importance", but listed the first postoffice, Antrim, 1840–1857; New Texas, a hamlet, in the geographic center of the township with "the usual mechanics, local stores, etc.", post office from 1856; and Logan's Ferry, on the Allegheny River and Allegheny Valley railroad, in the northeastern part of the township, deriving its name from early settler Alexander Logan and family, post office from 1844.
n 1956 Plum Township re-incorporated as a Borough under the Pennsylvania Borough Code and is governed by the Council-Mayor form of government. The Mayor is responsible for the oversight of the police department and Council is charged with the operations of the Boro departments. Council appoints a Boro Manager to handle the day-to-day operations of the Boro.