If you are ever in the middle of Illinois...
This collection will blow your mind.  The old farmhouse tour is also excellent if you are a history buff.
In one of the photos the docent (Bill) is holding a fossilized mushroom: the only one I have ever seen.  There is also a fossilized dragonfly in perfect condition.  Mind blowing stuff from an around the world traveler, Lafayette Funk, collected in the 70s and 80s.