My wife and I just got back from an overnight on the Wilderness Trail in Meramec State Park, just outside of Sullivan, MO. It was our first time on the trail and I thought it was very nice. It's a 10 mile trail with multiple rustic camping areas along the way. There's plenty of interest as the trail changes from rocky to smooth pine needle-covered, and everything in between; with multiple creek bed crossings, caves, and some scenic views of the Meramec river along the way.
We camped at about the 5-mile mark. There was plenty of dead fall to have a nice fire all night, and we had the songs of coyotes and owls to listen to. The people were few and far between this time of year.
It was a great weekend! If anyone is interested in hiking or backpacking this trail and wants more info, feel free to ask.