Marion County was created in 1835 from a portion of the western part of Izard County. The new county was named in honor of General Francis Marion, a Revolutionary War general, referred to by the British as the “Old Swamp Fox.” The county seat, Yellville, was created when white Americans appropriated the cleared land and settlement of Shawneetown, which was abandoned by Shawnee Indians in 1832. A group of Shawnee had founded Shawneetown on the White River after being invited to relocate to the Ozarks by the Western Cherokee in 1817.
Sources: Wikipedia and The Encyclopedia of Arkansas History & Culture
Baxter, Searcy and Boone counties in addition to the Missouri counties of Ozark and Taney.