Nice State Park. I grew up in the area and camped there so took the kids there on a trip while passing through the area. They have paved everything since I was a kid which is nice. There are several small lakes to fish and one lake has a nice swim beach. There are also Union Pacific Cabooses that are fully self contained you can rent to stay in. Some sites are right on the Platte River, but not much of a river in August. Sites are well spaced and pretty roomy. Restrooms and showers were pretty clean too.
This is a very scenic little campground. Most of the sites have permanent campers installed. 12 sites are available for overnight. You check in at their bar. The restrooms were vault toilets that smelled pretty bad. I did not use their showers, but it was reported to me that they were not clean and cost to take a cold shower. They have electricity available, but my site shared a 20 amp breaker with the site next me. You could not run very many things with the camper next to you plugged in without blowing the breaker, and using the a/c is out of the question. Fortunatly, one of the employees showed me where the main breaker panel was so I could re-set it when needed. Our site was about 50 feet from a nice little swim beach, but it gets crowded on weekends from the locals coming there. Overall, I might stay there again if I'm in the area.
This is a beautiful Forest Service Park up in the Roosevelt National Forest. Several sites sit real close to West Lake, which is a very nice little lake. A lot of people come there to fish. Most of the sites are pretty large, but only electrical. This year they removed the hose bib from the water faucets, so if you wanted to fill your camper's tank, you had to cut the hose to push it over the end of the faucet. There is no dump station either, so you need to plan on driving back into Fort Collins or so to dump your tanks. Overall a very nice relaxing place to go for a long weekend.
We camped here last month while visiting the Mount Rushmore area. It is a typical KOA, in that the sites are pretty much jammed together. I would recommend that you get a site as far away from the main road as possible as it is very busy during the summer and the heavy traffic seemed to ignore the 10 mph speed limit. My kids loved the water slide they have which cost an extra $10 per day to use for the whole family. They also have horseback riding available for somewhat reasonable prices.