Is there a route from central Illinois to southwestern Michigan that bypasses Chicago traffic?
Do you have access to a paper map or google maps (on a computer)?
72 to 74 to 41 to 65 will take you to Gary IN or you can take 94 to southwest Michigan. Obviously if you're going in the afternoon you'll still hit outbound rush-hour.
There are other two lane roads that will take you farther east, just check on a map or google .Edited: 22 June 2017, 23:00
East to US41
US 41 north to US 24
East on US 41 and then go north
US31 goes north but it all depends on where your final destination is
Or pick up 24 east on any route going north and follow to 421 north bound to 94. Two laners with slower speed limits though. Chances are your going to spend more time trying to avoid Chicagoland than just driving through it. (except possible rush hours) but the drive would be nice.
You don't need to take any of these.
From Decatur, just take #I74 NB until you get to #24. Take it EB until you get to #421 NB go north to #10EB. Take it to #35 NB to LaPorte. Then #39 NB. Goes right into New Buffalo, MI, from the south.
I won't say that you won't run into Chicago-type traffic up in New Buffalo, if you are traveling on the weekend, particularly returning on Sunday afternoon into evening.Edited: 26 June 2017, 02:12
Now that I think about it...If you are OK with not stopping for eating, etc. when you get that far north in Indiana, when you are taking #10, just take #39 NB. I mentioned #35 because it goes through both Knox and then LaPorte.
#39 is mostly country driving. Unless, of course, you want to visit the metropolis of Toto. ;)