Marion County is a county in the U.S. state of West Virginia. As of the 2020 census, the population was 56,205. Its county seat is Fairmont. The county was named in honor of General Francis Marion, known to history as "The Swamp Fox". Marion County comprises the Fairmont, WV Micropolitan Statistical Area, which is part of the larger Morgantown–Fairmont, WV Combined Statistical Area.