This is a fairly common occurrence and if we organized something for every fairgrounds we've had to deal with, we'd never have time for anything else!
I'll see if I can find a contact. Or, if you have one, PM me with it.
To answer your question, if the grounds are owned by the county, then 9.68 applies and they cannot post the grounds
. They can post buildings that are not restrooms or parking areas. There are some tricks that the Fair Boards have tried in order to avoid being covered by 9.68 that I will not go into on an open forum.