Pitcairn is a borough in Allegheny County, Pennsylvania, 15 miles (24 km) east of Pittsburgh, named for Robert Pitcairn, an official of the Pennsylvania Railroad.
Early in the 20th century, Pitcairn was the site of large railroad yards and shops that employed nearly ten thousand men. The population increased from 2,601 in 1900 to 6,310 in 1940, but has since declined. The population was 3,294 at the 2010 census.
As of the census of 2000, there were 3,689 people, 1,675 households, and 911 families residing in the borough. The population density was 6,892.2 people per square mile (2,637.6/km2). There were 1,901 housing units at an average density of 3,551.7 per square mile (1,359.2/km2). The racial makeup of the borough was 98.10% White, 0.43% African American, 0.11% Native American, 0.41% Asian, 0.05% from other races, and 0.89% from two or more races. Hispanic or Latino of any race were 0.54% of the population.
There were 1,675 households, out of which 24.7 percent had children under the age of eighteen living with them, 35.9 percent were married couples living together, 13.8 percent had a female householder with no husband present, and 45.6 percent were non-families. Of all households, 39.3 percent were made up of individuals, and 14.6 percent had someone living alone who was sixty-five years of age or older. The average household size was 2.20 and the average family size was 2.98.