Another good overnighter is Kissimmee River State Park, Buster Island Loop. It's a 6 mile loop though scrub oak, pine forest, and Oak Canopies. The primitive site is 3 miles in with 2 fire pits and picnic tables. There is no water available along the trail so you have to pack it in.
All of the Withlacoochee State Forest loops are great. My fave? Hard to say, really. But it depends on if you want a primitive campsite or not. If you are looking to stay in a campground, Citrus is the place to go. If that's the case, hike the "A" loop, or the "A/B" loop and afterwards crash at the campground, complete with electric, running water, and warm showers!
Citrus, Richloam, and Croom all have good primitive sites. I like 'em all!
I wish I could help. My buddy and I have been looking for the same thing. I've found some where you hike in and then hike back out, but I'd rather do a loop, too.
I live in Lake County close to the Withlacoochee State Forest, Richloam, Green Swamp, etc. Sandra has hit the nail on the head. Check out Wekiva Springs State Park and Lake Louisa State Park as well. These are two of my favorites to hike due to very different wood lines, prairies, scrub lands, and terrain. The list goes on at these two and not to mention a swim at either one. If you are in Lake County or Orange county let me know and I will hit the blaze trails with a member.
I recommend the primitive site camping at J.B. Starkey Wilderness Park in New Port Richey, FL. It has a 13 mile loop and has 3 primitive campsites along the trail. Each campsite has a fire ring and a picnic table (but no running water).