[1] The county was named in honor of Francis Marion, a brigadier general of the American Revolutionary War, known as the "Swamp Fox".

In 1803, most of the land for modern day Kansas was acquired by the United States from France as part of the 828,000 square mile Louisiana Purchase for 2.83 cents per acre.

The first settlers in Marion County located on Doyle Creek, near the present site of Florence.

The trail started in Texas and ended in Abilene, Kansas, where cattle were shipped eastward by rail.

[8] The south-eastern border one mile "notch" with Chase County was established under unusual circumstances.

A high wall for a place of refuge and defense in the event of an Indian attack surrounded it, but it was never needed for that purpose.

In 1871, the railroad pushed westward from Emporia through Florence, Horners, and Peabody towards Newton, and got title to the land in 1873.

[12] The original branch line connected Florence, Burns, De Graff, El Dorado, Augusta, Douglass, Rock, Akron, Winfield, Arkansas City.

In 1887, Atchison, Topeka and Santa Fe Railway built a branch line from Neva (3 miles west of Strong City) to Superior, Nebraska.

This branch line connected Strong City, Neva, Rockland, Diamond Springs, Burdick, Lost Springs, Jacobs, Hope, Navarre, Enterprise, Abilene, Talmage, Manchester, Longford, Oak Hill, Miltonvale, Aurora, Huscher, Concordia, Kackley, Courtland, Webber, Superior.

[citation needed] As early as 1875, city leaders of Marion held a meeting to consider a branch railroad from Florence.

The original branch line connected Florence, Oursler, Marion, Canada, Hillsboro, Lehigh, Canton, Galva, McPherson, Conway, Windom, Little River, Mitchell, Lyons, Chase, Ellinwood.

[citation needed] In 1887, the Chicago, Kansas and Nebraska Railway extended its main line from Herington to Pratt.

[15] This main line connected Herington, Ramona, Tampa, Durham, Waldeck, Canton, Galva, McPherson, Groveland, Inman, Medora, Hutchinson, Whiteside, Partridge, Arlington, Langdon, Turon, Preston, Natrona, Pratt.

[15] This branch line connected Herington, Lost Springs, Lincolnville, Antelope, Marion, Aulne, Peabody, Elbing, Whitewater, Furley, Kechi, Wichita, Peck, Corbin, Wellington, Caldwell.

The "Rock Island" has switches in Peabody and Lost Springs to allow connections to the crossing "Santa Fe" railroad in each city.

Both Santa Fe and Rock Island offered round trip fares from Chicago and western cities to Chingawasa Springs.

An economic panic in 1893 closed down the health spa and hotel, and quarry business along the tracks never developed sufficiently.

[16][17] The National Old Trails Road, also known as the Ocean-to-Ocean Highway, was established in 1912, and was routed through Lehigh, Hillsboro, Marion, Lost Springs.

The influence of the petroleum industry remained strong in Peabody, and resulted in the greatest change upon the community in the shortest time.

[19][20] In 2010, the Keystone-Cushing Pipeline (Phase II) was constructed north to south through Marion County with much controversy over road damage, tax exemption, and environmental concerns (if a leak ever occurs).

[26] This wind farm is located between Peabody, Aulne, and Florence, and operated by Ørsted headquartered in Fredericia, Denmark.

[39] † means a community is designated a Census-Designated Place (CDP) by the United States Census Bureau.