Philadelphia is the largest city in the U.S. state of Pennsylvania and the sixth-most populous U.S. city. Since 1854, the city has had the same geographic boundaries as Philadelphia County, the most populous county in Pennsylvania, and the urban core of the eighth-largest U.S. metropolitan statistical area. Philadelphia is also the economic and cultural center of the greater Delaware Valley along the lower Delaware and Schuylkill rivers within the Northeast megalopolis. The Delaware Valley's population of 7.2 million makes it the eighth-largest combined statistical area in the United States.