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".

Fairmont is a city in and county seat of Marion County, West Virginia, United States. The population was 18,313 at the 2020 census, making it the eighth-most populous city in the state. It is the principal city of the Fairmont micropolitan area, which includes all of Marion County in North Central West Virginia and had a population of 56,205 in 2020. Fairmont is also a principal city of the larger Morgantown–Fairmont combined statistical area.