Pen Argyl is a borough in Northampton County, Pennsylvania. The borough's population was 3,510 as of the 2020 census. Pen Argyl is located 26 miles north of Allentown. It is part of the Lehigh Valley metropolitan area, which had a population of 861,899 and was the 68th most populous metropolitan area in the U.S. as of the 2020 census.