For some specifics:
The Des Moines West KOA in Adel, IA is nice. It's off the highway a few miles to the north, so you don't hear the road noise. Nice sites, some are a bit tight though. Nice facilities for an overnight stay, have been there a few times.
The West Omaha/NE Lincoln KOA in Gretna, NE was good for an overnight stop. Good pull thru level sites, but it's fairly close to the interstate so there is some road noise.
There's a KOA on the east side of Cheyenne, WY, which is easy on/off from I-80. There's also a KOA in Laramie, WY right off I-80, but you will definitely hear the road noise there. Both are fine for overnight, the Laramie KOA has some nice pull thru sites, and the last time we stayed there, it was clean and the staff was helpful.
All of the above mentioned KOAs are fairly typical of what one might expect from KOAs. All of them had clean restrooms the times we stayed there, and generally friendly, helpful staff.