I'm in the Geneva area and am looking to put together my first carbonation system. It would be great to have a list of area shops that fill and/or sell tanks. I'm looking at a 5lb tank right now.
Illinois Fire and Safety 530 Lark Street, Unit C, Geneva, Illinois 60134 http://www.illinoisfire.com/contact.html
I go to the Addison Location I think it was 18$ to fill and took maybe 10 min. I don't know if they sell tanks. Air Gas in West Chicago is 28$ for a swap.
Wow. We sell a 5lb for $9.95, a 10lb for $12 and a 20lb for $14, but I'm in Louisiana so that doesn't really help you out. The only company that I know of even remotely close to you is Indiana Oxygen... but as the name implies, they're in Indiana (http://www.indianaoxygen.com/locations/).
FWIW, I'd look into getting a 50lb tank and a means to transfill into smaller tanks. It'll cost a bit up front, but it will save you loads in the long run. Actually, that's exactly what I am going to do.