I think you should find a good selection of choruses in the Chicago area. We mostly perform in the Baltimore/Washington area, but do get out on occassion.
Two concerts of note are this coming March 16, 2002 we are at the Meyerhoff Symphony Hall with Peter Schickele (aka PDQ Bach); and next March 30, 2003 we'll be at the new Murphy Fine Arts Center at Morgan State University with Dave Brubeck; and a lot in between. The website has more information.
We also perform with other groups like the Baltimore Symphony, National Symphony at the Kennedy Center, and other area concert venues like at Johns Hopkins University, plus area churches, but those concerts are on their schedules.