In search of overnight stop in IA or MO?

I'll second Wallace SP and add Watkins Mill SP just a little farther down I-35.

Eagle Ridge RV park in Eagleville, MO, just south of the IA/MO state line. 3 mins off the interstate, and a very nice couple runs this Ma/Pa CG. $30 FHU with a very clean pool and other facilities.

I assume you will be coming south on I-35. I would suggest Wallace Sate park. It has electric hookups and not far of I-35. While we haven't stayed in this particular park, we have stayed at 3 other Missouri State park Campgrounds and they were all very nice and reasonable in price.Last year we stayed at Pershing State park and it was $19 a night with electric.

Downstream Casino outside of Joplin, 3 free nights with players card

Slip Bluff County Park is halfway. Slip Bluff Just a few miles north of the state line, get off I-35 at US-69 (Lamoni IA) exit. Go west to the first paved road heading north and turn R. onto it. It will T out (end) at J52, turn right (keep an eye peeled for horses and buggies) and go under (or over? I forget) the overpass. Take the next left, Slip Bluff Road, and follow this road; it starts out going due north but then meanders east, then north, around a little lake before you come out at the campground.

I've been to this place twice and would happily stay there again if I were headed that way. The first time I was all alone there, and the second time I think a half dozen other campers were present. Level sites with electric, and there are water spigots scattered around. There's a nice view, too. One can walk along a trail westerly down the hill to the "Mormon Trail State Historical Marker." Nighttime lights of traffic can be seen in the distance (2-3 miles' worth) on I-35 to the north, yet because of distance and the trees between the CG and highway, very little road noise is heard.