- Philadelphia, colloquially referred to as Philly, is the most populous city in the U.S. state of Pennsylvania and the sixth-most populous city in the United States, with a population of 1,603,797 in the 2020 census. The city is the urban core of the larger Delaware Valley, also known as the Philadelphia metropolitan area, the eighth-largest metropolitan region in the nation with 6.245 million residents in its metropolitan statistical area, and 7.366 million residents in its combined statistical area.