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. Plum Borough was founded as Plum Township in 1788 and was reorganized as a borough in 1956.
According to the United States Census Bureau, the borough has a total area of 29.0 square miles (75.1 km²), of which, 28.6 square miles (74.2 km²) of it is land and 0.4 square miles (1.0 km²) of it (1.34%) is water.
There were 10,270 households out of which 34.1% had children under the age of 18 living with them, 63.6% were married couples living together, 8.5% had a female householder with no husband present, and 25.1% were non-families. 21.5% of all households were made up of individuals and 8.6% had someone living alone who was 65 years of age or older. The average household size was 2.60 and the average family size was 3.06.
In the borough the population was spread out with 24.8% under the age of 18, 6.1% from 18 to 24, 31.1% from 25 to 44, 24.8% from 45 to 64, and 13.2% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 95.4 males. For every 100 females age 18 and over, there were 91.9 males.
The median income for a household in the borough was $48,386, and the median income for a family was $52,807. Males had a median income of $40,788 versus $27,722 for females. The per capita income for the borough was $20,863. About 4.0% of families and 5.3% of the population were below the poverty line, including 6.0% of those under age 18 and 7.8% of those age 65 or over.
Pat McAfee, number one kicker for the West Virginia Mountaineers football team played for the Plum Mustangs.