Allentown (Pennsylvania Dutch: Allenschteddel, Allenschtadt, or Ellsdaun) is a city in Lehigh County, Pennsylvania. The city has a population of 125,845 as of the 2020 census. It is the fastest-growing major city in Pennsylvania and the state's third largest city, behind Philadelphia and Pittsburgh. It is the largest city in both Lehigh County and the Lehigh Valley, which had a population of 861,899 and was the 68th most populous metropolitan area in the U.S. as of 2020. Allentown was founded in 1762 and is the county seat of Lehigh County.