John - I found this campground on the state parks Web site, and I tent camped there in February 2004.
Campground Review
O'Leno State Park has two camping loops, the Dogwood and the Magnolia, and we much prefer the Magnolia because most of the campsites are larger and more private than those on the Dogwood. Also, it is closer to most of the trailheads and to the river access. The bathhouses were old and small when we camped here, but new bigger ones were in the process of being built.
As far as the park is concerned, O'Leno is an ideal destination for outdoor lovers. It is adjacent to River Rise State Park, so the two of them effectively make up a single preserve. The Santa Fe River runs through here, and it makes a peculiar spectacle by dropping underground in O'Leno (at a place called "the sink") and then flowing underground for three miles before resurfacing in River Rise and continuing to the Suwannee. Both "the sink" and "the rise" can only be reached by foot. The river is a good one for paddling.
There are over 13 miles of trails in O'Leno, all used by hikers and some also popular with mountain bikers. Additional trails in River Rise include more than 20 miles of bridal paths, at least some of which lead to a barn in the woods where equestrians can camp. As for wildlife, we saw three deer when we went on a nighttime hike. We had robins and woodpeckers on our campsite all weekend, and we saw a flock of sandhill cranes fly overhead one morning. And there were so many large turtles basking along the banks of the Santa Fe that I don't think I'm exaggerating when I say there were over 100 of them just within sight of "the sink."