Day 1: I-44 to St. Louis, I-70 to Effingham, IL 316 miles
Camping: Camp Lakewood CG, Effingham, IL
Camp Lakewood Central & Southern Illinois Campground - Homepage
Day 2: I-70 to Columbus, OH 317 miles
Camping: Alton RV Park, Galloway, OH
https://www.altonrvpark.com/
Day 3: I-71 (and I-271 around Cleveland) to I-90
I-90 to I-190 at Buffalo, NY. Follow I-190 to
Niagara Falls. 350 miles
Camping: Lots of choices in this area. I would
not recommend the one we stayed at (can't remember
the name, but it bills itself as the "closest to the falls"
on the US side. I have heard that there are some beautiful
campgrounds on the Canadian side
Maybe somebody can chime in with recommendations for a good CG in Niagara Falls...?