Berkeley County is located in the Shenandoah Valley in the eastern panhandle region of West Virginia in the United States. The county is part of the Hagerstown–Martinsburg metropolitan area. As of the 2020 census, the county population was 122,076, making it the second-most populous of West Virginia's 55 counties, behind Kanawha County. The City of Martinsburg is the county seat.

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.