Bill Pettit already answer about the local and state law side of the question.
I believe your answer lies in whether or not the fair is considered a private or public function. Is it free admission or did you pay and entrance fee? That may be the litmus test.
After that, who is offering the fair? Is it the county, state or other public entity? If so, regardless the entrance fee, it may be considered a public event and you cannot be restricted from photographing any more that you can from a public sidewalk.
Similarly, is it held on public property that is open to public access at other times? If so, it may be that you cannot be restricted from photographing unless the local or state law has a clause pertaining to leasing of public property for private use.
But, if the fair is organized and offered by a private for profit entity, then you might be restricted like at a concert in a public stadium where copyright issues of the performers are at play.
Peace! Sidney
