Marion county is in the Western Knobs region of Kentucky. The elevation in the county ranges from 475 to 1260 feet above sea level.
In 2010 the county population was 19,820 in a land area of 343.01 square miles, an average of 57.8 people per square mile.
The equine population was 2,000 in the 2012 Kentucky Equine Survey.
Marion county is was named for General Francis Marion, who served in the American Revolution.
Many early settlers were Roman Catholic and the first Roman Catholic church in Kentucky was built in 1792 in what is now the town of Holy Cross. The Sisters of Loretto convent is also located in the county in Nerinx.