Marshall County is a county in the U.S. state of West Virginia. At the 2020 census, the population was 30,591. Its county seat is Moundsville. With its southern border at what would be a continuation of the Mason-Dixon line to the Ohio River, it forms the base of the Northern Panhandle of West Virginia. Marshall County is part of the Wheeling metropolitan area. Marshall County is home to the largest conical burial mound in North America, at Moundsville.