  marion county is a county located in the u.s. state of ohio. according to the 2010 census, it has a population of 66,501, which is an increase of 0.4% from 66,217 in 2000. its county seat is marion. the county is named for general francis "the swamp fox" marion, an officer in the revolutionary war.  marion county comprises the marion, oh micropolitan statistical area, which is also included in the columbus-marion-zanesville, oh combined statistical area. ==geography== according to the 2010 census, the county has a total area of , of which  (or 99.91%) is land and  (or 0.09%) is water. ===adjacent counties=== *crawford county (northeast) *morrow county (east) *delaware county (south) *union county (southwest) *hardin county (west) *wyandot county (northwest) ==demographics== {{uscensuspop |1830=6551 |1840=14765 |1850=12618 |1860=15490 |1870=16184 |1880=20565 |1890=24727 |1900=28678 |1910=33971 |1920=4200
1820_establishments_in_the_United_States Columbus,_Ohio_metropolitan_area Marion_County,_Ohio Ohio_counties Populated_places_established_in_1820