Yes, the Chicago Critical Mass meets on the last Friday of the month, Daley Plaza, Dearborn & Washington. 5:30pm is the posted time, but it's generally 6:00pm when the ride starts. (The half hour in between is a fun time for conversation, admiring unusual bikes or costumes, voting on which of the map routes to follow, getting party favors, etc.) The next two will be September 28th and October 26th. The October 26th one will probably be the Halloween ride, and a lot of riders tend to show up in costume.
I'm still a car owner myself, and I would not place you in the same category as the SUV owner that I described. Wisconsin is a pretty place to go to. There is no official party line that a person has to follow in order to be a part of Chicago Critical Mass. There are those who are anti-cars, and there are those who use cars quite a bit. (One person I know, for example, drives his car in from Indiana in order to get to Critical Mass.) A love of bicycling as a viable and fun means of transportation is the common link that we share.
The Chicago Critical Mass web site is
http://chicagocriticalmass.org/