Just came back from a nice weekend at Madison KOA. It's right off of I-90 just north of Madison, so you get a little highway noise, but not too bad. There's a Culvers, McDs, Arbys, and a Cheese store right across the road.
The owners were very friendly and they offered lots of activities for the kids - many of them were free. My kids (2 and 6) had a blast - especially on the inflatable horses
Plus they had breakfast for $2 (pancakes) and lunch for $2 (brat and chips), and were offering a wine and cheese tasting in the afternoon and had bingo with a free ice cream social afterwards (bring your own bowl and spoon).
We'll definitely head back!
Just edited to add - the showers were so clean and loved the large showerhead and a space to put your shampoo, etc!