Old fair grounds are one of the best places to find old coins. I once hunted a school here in Fl. and started finding silver from 1888 to 1934. Lot's of silver. I also found a class ring from 1932. I contacted the school to see if I could find the owner. The principal said the school was built on the old fair grounds and that's why I found so many old coins and yes, I did get to return the class ring.
The BIG problem is finding out where the grounds were. You can't google them because all you will get are the new fair grounds. If the library has micro film of newspapers you can search there for stories about the fairs but a lot of the time you won't get an address...