Pittsburgh ( PITS-burg) is a city in the state of Pennsylvania in the United States, and is the county seat of Allegheny County. A population of about 300,286 (2019) residents live within the city limits, making it the 66th-largest city in the U.S. and the second-most populous city in Pennsylvania behind Philadelphia. The Pittsburgh metropolitan area is the anchor of Western Pennsylvania, its population of 2,324,743 is the largest in both the Ohio Valley and Appalachia, the second-largest in Pennsylvania, and the 27th-largest in the U.S.
Pittsburgh is located in the southwest of the state, at the confluence of the Allegheny, Monongahela, and Ohio rivers. Pittsburgh is known both as "the Steel City" for its more than 300 steel-related businesses and as the "City of Bridges" for its 446 bridges. The city features 30 skyscrapers, two inclined railways, a pre-revolutionary fortification and the Point State Park at the confluence of the rivers. The city developed as a vital link of the Atlantic coast and Midwest, as the mineral-rich Allegheny Mountains made the area coveted by the French and British empires, Virginians, Whiskey Rebels, and Civil War raiders.
Aside from steel, Pittsburgh has led in manufacturing of aluminum, glass, shipbuilding, petroleum, foods, sports, transportation, computing, autos, and electronics. For part of the 20th century, Pittsburgh was behind only New York City and Chicago in corporate headquarters employment; it had the most U.S. stockholders per capita. Deindustrialization in the 1970s and 80s laid off area blue-collar workers as steel and other heavy industries declined, and thousands of downtown white-collar workers also lost jobs when several Pittsburgh-based companies moved out. The population dropped from a peak of 675,000 in 1950 to 370,000 in 1990. However, this rich industrial history left the area with renowned museums, medical centers, parks, research centers, and a diverse cultural district.
After the deindustrialization of the mid-20th century, Pittsburgh has transformed into a hub for the health care, education, and technology industries.