I'm one of the few in the area, here is the current state of rocketry in my general vicinity (in Manitowoc; on Lake Michigan between Milwaukee and Green Bay).
Clubs:
-Woosh & Tripoli Wisconsin Association (TWA): As others have said, the most active groups in Wisconsin are Woosh (NAR) and TWA (TRA) that both operate out of Bong in Southeastern Wisconsin.
-Tripoli Upper Michigan: Bill Bertoldi has a great little group that fly at the Groveland Mine site at Randville, MI. Unfortunately, Bill is losing his site after his June (14th if I remember correct) launch as they are re-opening the mine.
-LARS (Lakeshore Area Rocketry Society): I formed this club in 2006 or 2007. It grew and eventually became a NAR Section (LARS) and Tripoli Prefecture (Tripoli Manitowoc #120). LARS hasn't had a launch for some time and Tripoli Manitowoc lost its high power field and is essentially dead.
-Cool City Rocketeers: After I migrated away from LARS, there was still a group of loyal rocketeers in my area. We formally formed a NAR Section last year and have been operating out of the Two Rivers High School location on a fairly regular basis. We are an active Section; though we don't have a website. If you want "in" on launch announcements, send me an email and I'll put you on the list. We have the first launch of the season on Saturday, May 10th; it is a low-mid power launch only (3.3lbs rocket, 125g motor limit)
-If there are others, I don't know about them; and I do know of most rocketeers in the region in some shape or form.
-Eric-