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, MD-WV Metropolitan Statistical 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.