Only governments and government agencies can infringe on your constitutional rights. (Please insert here skidmark's standard rant about people who try to claim private businesses infringe on constitutional rights.)In 2002 it was decided the fair should become incorporated and it became a non-profit, 501[c] community organization.
As a private business, the The Caroline County Agricultural Fair Association can set up rules for entrace onto their property and your only options to abiding by them are to comply with them or commit trespass.
I happen to agree with your decision not to attend, but there is no way I can support your whinging about some violation of your "rights".