Lancaster County is a county located on the Northern Neck in the Commonwealth of Virginia. As of the 2010 census, the population was 11,391. Its county seat is Lancaster.Located on the Northern Neck near the mouth of the Rappahannock River, Lancaster County is part of the Northern Neck George Washington Birthplace wine-growing region recognized by the United States as an American Viticultural Area. Lancaster County is the most densely populated county in the Northern Neck.