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 Ma…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.