Plum is a borough in Allegheny County, Pennsylvania, United States. The population was 27,144 at the 2020 census. A suburb of the Pittsburgh metropolitan area, it is located northeast of the city in what is commonly referred to as the East Hills suburbs. 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.