Philadelphia - Wikipedia Philadelphia ( ˌ f ɪ l ə ˈ d ɛ l f i ə ⓘ FIL-ə-DEL-fee-ə), colloquially referred to as Philly, is the most populous city in the U S state of Pennsylvania [11] and the sixth-most populous city in the United States, with a population of 1,603,797 in the 2020 census