There are 2 campgrounds: the mixed use campground is gorgeous, nicely treed, some big spots. The park itself is huge and there is lots to do with kids, a lake to swim in, a nice playground, lots of walking trails, and a golf course with a clubhouse where you can buy lunch or snacks if you don't want to cook. The RV-only site is totally like a parking lot. We camped here in a Motorhome.
There are two campgrounds in Elk Island NP, both without hook-ups of any kind - one is for tents or trailers. It is the nicer of the two, with trees, fire pits, washrooms with lukewarm showers, and picnic table. It was rather empty when we were there, but it was during the week (we arrived on Monday, left on a Friday); we found good camping without a reservation but were told that they do fill on the weekends. The other campground is for RVs only, and is basically a parking lot with fire pits and picnic tables. It was empty when we were there, and it seems as if it would have a parking lot feel if it were full of RVers. We camped here in a Travel Trailer.
I think it was originally designed as a picnic area. Sites are extremely close together with virtually no privacy from your neighbor. The rates, while high enough, are misleading - it will cost you $7 per person, per day to enter the park gates, plus $7 per night for a fire permit. The access road through the park is long, and in very poor condition. We camped here in a Motorhome.