Allentown (Pennsylvania Dutch: Allenschteddel, Allenschtadt, or Ellsdaun) is a city in Pennsylvania and the county seat of Lehigh County, Pennsylvania, United States. It is the third-most-populous city in Pennsylvania with a population of 125,845 as of the 2020 census and the most populous city in the Lehigh Valley metropolitan area, which had a population of 861,899 and was the 68th-most populous metropolitan area in the nation as of 2020.Founded in 1762, Allentown is located on the Lehigh River, a 109-mile-long (175 km) tributary of the Delaware River. It is the largest of three adjacent cities, including Bethlehem and Easton in Lehigh and Northampton counties, in the Lehigh Valley region of eastern Pennsylvania. Allentown is located 48 miles (77 km) north of Philadelphia and 78 miles (126 km) west of New York City.