We are avid COE campers. I started my COE camping 50 years ago, and a few weeks ago we were at the first campground I ever went to camp.
The Corps publishes a paper map which shows all their projects across the country and which have campgrounds. The also have a CD available which has the same information as www.corpslakes.com - just static. You can usually get those at a Corps project office/ visitors center.
Unfortunately there isn't a good searchable web product if you want to filter by opening / closing dates. Which campgrounds have sewer connections, which have 50 amp, which have 30 amp, etc.
Recreation.gov will allow you to do some of those filters, but only for campgrounds with reservable sites. The COE has a lot CG that are not reservable.
If you have an idea of where you want to go, recreation.gov is an excellent tool. If you are just trying to see what is where, the corpslakes state maps are great.
Also, there are several lakes in the western US which are under the Bureau of Reclamation. The Tennessee Valley Authority has campgrounds, which are not in recreation.gov