The word appeared in the 1920s. Defined as an informal session, or as a gadget.
"American Speech," 1929: Meaning the same as gadget.
1940: "The New-Dealers' Midsummer Hootenanny."
Seems to me that trying to limit the definition ain't a-goin' to work. Certainly a barn dance is an informal gathering, and we used the word for that in the 1930s in the west. Coyote Breath, that is exactly the way we used the term. Set up a table for food and hooch in the barn (the only place on the farm big enough for dancing and general hoop-te-do), all the wives brought food, and some locals played for the dancing. Sometimes there was a bucket to collect donations.
Several people seem to have claimed the term, but probably their claims are based on wishing that they had coined it.