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.

Moundsville is a city in and the county seat of Marshall County, West Virginia, United States, along the Ohio River. The population was 8,122 at the 2020 census. It is part of the Wheeling metropolitan area. The city was named for the nearby ancient Grave Creek Mound, constructed 250 to 100 BC by indigenous people of the Adena culture.