[2] Marion County is named for American Revolutionary War guerrilla leader Francis Marion also known as The Swamp Fox.

[3] According to the U.S. Census Bureau, the county has a total area of 549 square miles (1,420 km2), of which 542 square miles (1,400 km2) is land and 6.2 square miles (16 km2) (1.1%) is water.

[4] As of the 2020 United States census, there were 24,441 people, 9,483 households, and 5,863 families residing in the county.

The Mississippi Department of Human Services's Division of Youth Services operated the Columbia Training School in unincorporated Marion County.

[17] The county is in the service area of Pearl River Community College.