The majority (like 90-95%) of OHV/ORV trails in Michigan will be pointless to run down for wheeling purposes. The ATV/ORV trails aren't wide enough to take anything bigger than a quad down (plus it's illegal to take your truck down them). The OHV trails that are legal to run are trails that any passenger vehicle can make it down, such as your average FWD compact car. Anything else is off limits. There are a few park sections that are open for wheeling, but few. Those few include The Mounds off road park in Mt. Morris (outside of Flint), Bull Gap (I believe it's in Rose city, but google it to be sure. I do know its in the northern lower peninsula), Silver Lake sand dunes, and Drummond Island (in Lake Superior, near St. Ignace). There is currently work being done to improve Drummond for wheeling, and serious work at that. Some of the people from Michigan Jeepers and Michigan Trail Conservation are involved in that, some of which I know personally, and know that they are serious about getting this done. There are also some people that have large plots of private land that they open to wheeling on a limited basis. One of the better ones is an annual pig roast hosted by Yogi and Grandman from Michigan Jeepers. It's largely a Jeep based event, but open to all four wheelers. You will get razzed heavily for showing up with anything buy a Jeep tho (personal experience...even tho I'm a former owner of several Jeeps, I still get ragged on for wheeling an Explorer now).
I'd love to hook up with some other X owners/wheelers for some trail riding in Michigan. Hopefully my X will be ready to roll in about a week, and be ready to rock in about a month. Really only need to the hubs to get it rolling, but still want to redo the bumpers, add rock sliders, mount the Hi-Lift and spare, redo the lights, etc....