We camped in April - in our teardrop trailer - and almost had the campground to ourselves!  Very few people and those that were there were very spread out.  Our site was right on the creek and it was a lovely sound for nighttime!  We had easy access to laundry if needed (at the next lodge down the road inside the park) and firewood was available there too for $6/bundle if you wanted it. Generally there is a restaurant during tourist season, but wasn't open yet. This campground - Game Lodge - was the only one in the park open at this time of year.  We went in early April. 

For those concerned about the animals - yes the deer can jump the fence into the campground, but notice I said "fence"...the bison can not get in.  Even with the gate open, there is a large "cattle grate" in the pavement to keep them from coming it.  They love to graze in the grass outside the fence, but can't get in.

All sites had a fire ring (we didn't use ours since it was VERY windy and VERY dry) but it's good size.  There are picnic tables at each site as well. Vault toilets as well as full bathrooms (heated) with showers for free (hot showers). The showers are not on all year long, but only when the frost is out of the ground for the water lines . Water spigots for drinking water are here and there, but again, only on when there is no danger of freeze.

Spaces were clearly marked, tent pads were raised on pea type gravel, cabins looked lovely (appeared to have A/C).