York County is the southwesternmost county in the U.S. state of Maine, along the state of New Hampshire's eastern border. It is divided from Strafford County, New Hampshire, by the Salmon Falls River and the connected tidal estuary, the Piscataqua River. York County was permanently established in 1639. Several of Maine's earliest colonial settlements are found in the county, which is the state's oldest and one of the oldest in the United States.