Jefferson County is located in the Shenandoah Valley in the Eastern Panhandle of West Virginia. It is the easternmost county of the U.S. state of West Virginia. As of the 2020 census, the population was 57,701. Its county seat is Charles Town. The county was founded in 1801, and today is part of the Washington metropolitan area.

The Shenandoah Valley is a geographic valley and cultural region of western Virginia and the Eastern Panhandle of West Virginia in the United States. The Valley is bounded to the east by the Blue Ridge Mountains, to the west by the eastern front of the Ridge-and-Valley Appalachians, to the north by the Potomac River, to the south by the James River, and to the Southwest by the New River Valley. The cultural region covers a larger area that includes all of the Valley plus the Virginia Highlands to the west and the Roanoke Valley to the south. It is physiographically located within the Ridge and Valley Province and is a portion of the Great Appalachian Valley.