is a city located in Lehigh County, Pennsylvania, United States. It is Pennsylvania's third most populous city and the 233rd largest city in the United States. As of the 2010 census, the city had a total population of 118,032 and it is currently the fastest growing major city in Pennsylvania with an estimated 121,442 residents according to the 2019 census estimate. It is the largest city in the metropolitan area known as the Lehigh Valley, which had a population of 821,623 residents as of 2010. Allentown is the county seat of Lehigh County. In 2012, the city celebrated the 250th anniversary of its founding in 1762.