Pittsburgh is the second-largest city in the US Commonwealth of Pennsylvania and the county seat of Allegheny County. Regionally it anchors the largest urban area of Appalachia and the Ohio River Valley and nationally it is the 22nd-largest urban area in the United States. Template:Geographic reference The population of the city in 2010 was 305 704 while that of the seven-county metropolitan area stood at 2 356 285.