Lancaster is a city in and the county seat of Lancaster County, Pennsylvania, United States. With a population of 58,039 at the 202…Lancaster is a city in and the county seat of Lancaster County, Pennsylvania, United States. With a population of 58,039 at the 2020 census, it is the tenth-most populous city in the state. It is a core city within South Central Pennsylvania, with 552,984 residents in the Lancaster metropolitan area.