It is thought to have originated with illiterate itinerant African American piano players, who learned the syncopated music not formally, but through their peers.
It was later revived, starting in 1947 with the 'rediscovery' of Sanford Brunson Campbell (March 20, 1884 - November 23, 1952) who was one of the most noted folk ragtimers as well as a student of Scott Joplin, and then in the early 1960s by the now foremost authority on Folk Ragtime, Trebor Jay Tichenor (1940-2014).
Good testimony of this are the legendary multiple takes of Folk Rags by Sanford Brunson Campbell, recorded on acetates in 1947.
In terms of melodic and harmonic content, Folk Rags have a distinct blues influence.
A typical chord progression in B♭ major would go: At the center of the revival of folk ragtime has been historian, collector, and composer/pianist Trebor Jay Tichenor.