Carnegie is a borough in Allegheny County, Pennsylvania, United States. The population was 8,134 in the 2020 census. It is part of the Pittsburgh metropolitan area. Carnegie is named after Andrew Carnegie, who donated one of his libraries for the gesture. It was incorporated on March 1, 1894, from the boroughs of Chartiers and Mansfield. Later, the bor…Carnegie is a borough in Allegheny County, Pennsylvania, United States. The population was 8,134 in the 2020 census. It is part of the Pittsburgh metropolitan area. Carnegie is named after Andrew Carnegie, who donated one of his libraries for the gesture. It was incorporated on March 1, 1894, from the boroughs of Chartiers and Mansfield. Later, the borough annexed part of Robinson Township. Neighborhoods include Rosslyn Heights, Cubbage Hill, Irishtown, Forsythe Hill, Library Hill, and Old Mansfield.