THat is a Huge understatement..
I suggest the Gurnee Mills Mall... It's next to Six Flags: Great America (my 1st job ). It's 15 minutes from the WI border, we can meet up there and us up in northern IL (me hopefully) can meet up with the Chicago and other smart drivers.
P.S. Just a warning, Gurnee's roads are an obstacle course...
Make you plans a bit further north for the northern Chicago up through Milwaukee. Even when 94 isn't under construction that area around Gurnee mills Mall is a nightmair and you would never keep a group together.
Try Location (26) for a grouping on I94
And those on 39/90 can regroup at (22)
SOURCE Rest areas in Wisconsin