Aloha...
I purchased the Fall Fountain County Fair boost from the last event and have not yet received it as a decoration. I bought it just about the time I started the event when the prompt came up (well before the expiration). I've restarted my device and checked my cellar several times and even deleted and reinstalled my game and it still has not shown up.
I play on an iPad (iOS 10.0.2), Game Version 2.5.1
In this screenshot you can see in the upper left hand corner that the Fall Fountain boost is active (not grayed out) as proof that I purchased it:
Any help would be appreciated. Mahalo