On the note of buying seed/stock, there are a lot of native seed suppliers in the midwest, especially for prairie work, but they'll have wetland stuff too. A quick scan of the back of an Ecological Restoration issue yields the Indiana nursuries:
Spence Restoration Nursery: www.spencenursery.com
JFNew: www.jfnew.com
(I have no experience with these two companies though, as their seed isn't appropriate for the southeast)
A lot of people use Earnst Conservation Seeds, out of Pennsylvania.
Also, I don't know if you've been to the Indiana Native Plant Society's website:
http://www.inpaws.org/ They will likely have a list of native plant sources.
Anyway, my point for adding this was that if you go to the website or get the catalog for these companies, sometimes they have advice on how to go about restorations. A nice thing about the Illinois companies would be that they might have advice that is specifically taylored to your area. If you google something like "Illinois native plant seed", I'm sure more companies will come up.
(Also, if you need material to keep the soil from washing out as your plants get established, or other such stuff, I often specify material from North American Green, and erosion control company www.nagreen.com. They make some stuff that is completely biodegradable. They also give good instructions! Depending on your conditions, (slopes?) you may not need stuff like this. I just thought I'd mention it.)