Eagle City Park has two parts - a lower campground that is a paddlers camp on the Iowa River, and an upper campground with a few secluded campsites.
All campsites are free, and there are many to choose from. I have camped in both the upper and lower campgrounds, in summer and fall. I tend to prefer off-season when I am (often) the only camper in either campground. Summer will have more campers, ranging from tents to small RVs, but there are plenty of campsites so it is never full.
There is nowhere to buy firewood, but a short hike in the woods usually produces a small supply for a campfire.
Negatives:
As there are no trash containers, it is not uncommon to find the firepits full of burned or unburned trash.
There is a very poorly kept vault toilet in the lower campground. I do not believe that it is ever pumped out. The upper campground has no toilet. I always bring my own stool "just-in-case" but otherwise just take care of business after I take the 20 minute drive to get home.
The gates are closed all winter, often into late spring. The roads are not plowed in either campsite. It is a nice place to hike in winter time, but there is no camping.