Bluegrassrivals

have anything that comes close to Hillbilly Days? I know the Ohio State Fair is pretty big, but anything else worth mentioning?

South Carolina does a big festival during the 4th of July. But its not that big.

Hillbilly Days is probably the biggest.

Louisville has Thunder Over Louisville at the same time as HBD every year, there are A LOT more people there in Louisville. It's way bigger than HBDays.

I know Louisville is technically still in this state, but I don't consider them part of KY, lol.

Some of the county fairs over here might qualify - haven't been to any myself, so can't say for certain, but Washington & Russell County both have concerts with "names", like Confed. RR, coming in to play. Also, down past Bristol is the Appalachian Regional Fair that is huge, and out near Roanoke is the Salem Fair, which is held around the 4th of July. Both of those have multiple "names" come in.
Lots of towns also have some kind of "festival" during the Summer (like Best Friends Days in Wise), but none come close to HD.