Easton is a city in and the county seat of Northampton County, Pennsylvania, United States. The city's population was 28,127 as of th…Easton is a city in and the county seat of Northampton County, Pennsylvania, United States. The city's population was 28,127 as of the 2020 census. Easton is located at the confluence of the Lehigh River, a 109-mile-long river that joins the Delaware River in Easton and serves as the city's eastern geographic boundary with Phillipsburg, New Jersey.