Marion is a home rule-class city in Crittenden County, Kentucky, in the United States. It is the seat of its county. As of the 2010 census, the …Marion is a home rule-class city in Crittenden County, Kentucky, in the United States. It is the seat of its county. As of the 2010 census, the city population was 3,039. The farm communities surrounding Marion are home to a large Amish population. The Marion-Crittenden County Airport is located west of the city.