York County is located in south-central Pennsylvania, United States. It is part of the Commonwealth of Pennsylvania and lies in the Susquehanna Valley region. The county is bordered to the northeast and east by the Susquehanna River, to the south by the Mason–Dixon line which separates Pennsylvania and Maryland, and to the northwest by the Blue Ridge Mountains and Yellow Breeches Creek. York city is the county seat of York County. The county is conveniently accessible from nearby cities such as Baltimore, Harrisburg, Lancaster, and Philadelphia, with major highways like I-83 running through it. York County covers an area of about 911 square miles, mostly land, and had a population of approximately 456,438 as of the 2020 census.