Marion is a city in and the county seat of Marion County, Ohio, United States. The municipality is located in north-central Ohio, approximately 50 miles north of Columbus. The population was 36,837 at the 2010 census. According to the US Census 2008 estimate Ohio's Columbus–Marion–Chillicothe Combined Statistical Area has 2,002,604 people. Marion is the county's largest city and the center of the Marion Micropolitan Statistical Area. President Warren G.