Found this post after I'd IM'd Vandal. I'm from Lebanon TN. Got my ATV to use specifically for duck hunting in flooded rice fields in Arkansas but I find its so much fun that I can't stay off of it. I "aerated" my yard this past weekend with my new tires. . . lol!
I've been to the Covington Pike bottoms area in Memphis. It's not any type of official ATV trail or even sanctioned for riding, it's just one of those places folks go. It's in a high crime area, there are burned out cars, piles of trash, but if you want mud, that's the place. There are lot of mudders that go there and plenty of trails to keep you busy all day. You'll see lots of snorkeled ATVs there. If you go, someone there will tell give you tips and tell you about the trails. When a buddy and I went there for the first time, someone chased us down and warned us that we needed to improve the security of our trailer, so we chained it to the fence. If you go through mud holes, be sure you have a buddy to winch you out. There is a facebook group called "Covington Pike Mud Slingers" that posts some pics and tips for riding there.
I've also been to Natchez Trace State Park just off of I-40. It's got some fire roads and trails. Parking is tight, you can park your truck/trailer just off the road on the fire trails. Some trails were developed by riders off of marked trails. It's enough to keep you busy for half day. A good place for young riders. Also a good place to break in an ATV. There is a buried gas pipeline that goes through the park. ATVers have used that but it's posted not for trail rides. (that looks like the most fun of all though). There are trails on both sides of the interstate. Don't get caught on the pavement.
I've been wanting to try Turkey Bay Off-Highway Vehicle area. Also, I'd like to try Windrock sometime. Never been to either. Open for a Mid-Tn trail ride sometime.