Look up gun ranges, then call and see if you can shoot a shotgun there. Also try DNR website. Also asking around people in your local area. I am guessing you could find some state land. Might not have shooting benches. Some DNR places may have benches.
Also if you contact a sportsman club they could advise you, without joining. Other thing would be to find gun or hunting forum with IL section and ask. But probably better to just ask someone nearby.
Then you have to decide how what range. Are you using a scope? What yardage do you want it zeroed? Sometimes people have it high at one yardage so it is good further out. I like to play with Nikon Spoton. You can enter a bunch of brands ammo, and what range you want to be zeroed and will show you path. If you know for sure will be shooting at 30 yards, I would just site for 30 yards.
Need to steady yourself to site in. You are not their to practice, but get the gun dialed it. I used to kneel over atv. I have done bipod and kitchen chair. I have portable bench. Even leaning against tree helps. Better rest more accurate you can get it sited in.
If you get bad results with one brand try another. Sabots are for rifled barrel slugs for smooth barrel.