Okay, here's the list. I'm in C'ville myself and have been compiling the local groups as I find them...
Elgin Mom's meetup:
http://moms.meetup.com/1098/
Haven't been a member of this one long, but so far they have seemed like a great bunch of women.
Cary Mom's meetup:
http://moms.meetup.com/1183/
This group might be fading away, and hasn't had many of it's own events since many members moved to another site off meetup.com, listed next.
Cary Moms Group:
http://www.carymomsgroup.com/
This group moved off meetup.com a while ago and has been thriving. Lots of great events, and people. They also have activities for dads and playgroups.
Suburban Chicago Mom's meetup:
http://moms.meetup.com/1712/
This is a more generalized group for the northern/northwest suburbs of Chicago. Recently moved when the previous group narrowed down to just one area, this is an active bulletin board online, with some gatherings that move around to different play places throughout the suburbs.
Parents Who Care:
http://parentswhocare.org/
Another group centered around the Hoffman Estates/Schaumburg area, this group offers an awesome Summer Camp and several other activities that make it worth joining. Another great bunch of people. This group is well-organized with a board and budget, and they hold fundraisers and resale events during the year too.
There is also a Mom's Club of Carpentersville group too, although I can't seem to find their link on meetup.com at the moment. I've been in contact with them, but haven't actually met with them yet to join so I can't say much about them.
Feel free to drop me a message if you want more info on any of these. :-)