Just outside of Macclenny Florida. St. Marys Shoals Park in Baker County.
https://www.facebook.com/pages/St-Marys-Shoals-Park/361758947235237http://www.sfrc.ufl.edu/CFEOR/docs/Understanding%20the%20Human%20Dimensions%20of%20OHV%20Recreation%20on%20the%20Ocala%20National%20Forest.pdf It has less than 20 miles of trails to ride on and doesn't offer much for excitement such as hills, banked curves, water or muddy trails.
On the other hand it is a great place to take young kids to ride on smooth flat trails with a 25 MPH speed limit. It is only open on Saturdays and Sundays 8 to 5. The trail head has a large parking lot and nice restrooms.
If you live more than a hour away you might spend as much time driving back an forth as riding trails. If you go there I would recommend spending the weekend at
http://www.soggybottommp.com/index.php and ride both areas as they are pretty close together.