Marion is a city in Marion County, Ohio, United States, and its county seat. It is located in north-central Ohio, approximately 50 miles (80 km) north of Columbus. The population was 35,999 at the 2020 census, down slightly from 36,837 at the 2010 census. It is the largest city in Marion County and the principal city of the Marion micropolitan area. It is also part of the larger Columbus–Marion–Zanesville, OH Combined Statistical Area.