Yes you are right, at the rockford field, you must join their rc club plus buy the permit and have your ama.
At Kieselburg, on Swanson Rd., (north of Machesney Park), you buy the permit and you have your ama. There isn't a club there, just some guys that show up to fly.
Cost
Rockford permit for non residents is like $60 for the year plus I think $30 for the club plus ama.
Kieselburg permit for the forest preserve is like $30 for the year plus your ama. There isn't a club
Two totally different fields over here. If you do a search for flying fields here, the rockford field is the only one that comes up. You have to search specifically for Kieselburg to find it. And from Capron it's only about a 20 min drive, I think, I'll have to check on that.
We don't have a real big field but I think you could fly a bird with 7ft wingspan ok. Most guys fly 6ft or less. Most fly electric power, only a few of us still fly glow. And a couple guys fly the big 3D birds and they're on their tail most of the time.
It's not a bad field. I'm sure I could fly a 1/4 scale Cub there but I wonder about a 101in Bud Nosen Big Stik, or a 1/3 scale BUSA Der Jager. Those two I think will be to big to fly there. We'll see.