Here’s a page that lists some places to find fossils in Ohio.  I’m not sure the trilobite on the page is correct… looks like an Elrathia kingii.  The one above is from Ohio and is a Flexicalymene.  But, the page has a nice list of places to go and what you can find.  Trilobites are a big part of what you can find… Check it out!

Southwestern Ohio

• Caesar Creek State Park (Warren and Clinton Counties) – requires permit, which is available free from the U.S. Army Corps of Engineers Visitor Center.
• Cowan Lake State Park (Clinton County)
• East Fork State Park (Clermont County)
• Hueston Woods State Park (Preble and Butler Counties)
• Oakes Quarry Park (Greene County)
• Stonelick State Park (Clermont County)
• Trammel Fossil Park (Hamilton County)

Northwestern Ohio

• Fossil Park (Lucas County)