Under the existing rules, from the official page, the prohibition on firearms does not apply to:
Exceptions to the above prohibitions are limited to:
Weapons of OSF law enforcement officials and those carried by persons authorized by law
to carry them when carried in a manner authorized by law;
While state fair personnel may not realize that their own rules specifically allow weapons that are lawful, they do. And since no CHL is required to openly carry, it would seem that open carry without a CHL (and loaded) is also "authorized by law" and therefore not prohibited.
HOWEVER:::::: Be very cautious of the "public building" restrictions for non CHL holders who are open carrying.
But if you don't push the issue, I'm guessing they'll try to turn you away hoping you don't know the law and THEIR OWN RULES.