Out here in the west, Labor Day weekend is anything but quiet at most places to camp, commercial or otherwise. It marks the end of the season for a goodly number of places here in Colorado. I was at Glacier Basin in Rocky Mountain National Park this past weekend, it was completely full; they are only open 2 more weekends and then it's end of the season for them. Went past Elk Meadows Resort (commercial CG in Estes Park CO), they too were just about completely full, and will likely be that way until they close in October.
Many places out here start to close down shortly after Labor Day. Much of that is due to elevation. USFS CGs are dependent on snow and cold to determine when they close. Some close early; at lower elevations they close later. Commercial CG start to close around the middle of September, to mid-October out in this area.
I know you mentioned a tri-state area back in the Midwest, and KOAs. I would venture to say that many places back east that are popular camping spots will be like here in Colorado -- full and less than quiet. Guess it depends on what amenities/sights are in the area to make them popular.