There are many options:
#1 SMORR - Southern Missouri Off Road Ranch - Seymour, MO. SMORR, Southern Missouri Off Road Ranch - Home
#2 Joe State Park | Missouri State Parks
#3 Flatnasty next to Salem MO
Welcome to Flatnasty
#4 Washita next to Farmington MO
Washita Off-Road Trails
#5 Potawatomi Offroad Park 7 miles north of Kingdom City Capital City Crawlers
#6 Sayers Brook Potosi MO
SayersBrook Off Roading
Take Your Pick. Keep an eye on the Missouri Forum (KC, STL, OZARK) for upcoming trail rides.
#5 Potawatomi SUCKS! and #6 Sayersbrook Bison Ranch only allows organized trail rides with groups. The rest are fine.
If you just like a nice drive off paved roads there is the Palmer Lake area in the Mark Twain National forest near Potosi, MO or you can try the Lost Creek Road that goes from the Foristell/Warrenton, MO area towards Hermann, MO