For the drive in from O'Hare, I suggest the following:
IL:
Starcom21 towers for Cook county. Counties listed for towers.
IN:
Safe-T towers for Lake, Porter, and La Porte counties. Counties listed for towers.
The above should cover I-94 until you get to Michigan.
While in MI:
You already figured out that quite a bit is on MPSCS, the state's digital system. In Berrien County, the following can still be found on analog (note that some of the below do both depending on the circumstances), and what is in the database for them should be correct:
- County fire
- Saint Joseph (city), Benton Harbor, and Benton Township. These are fairly close to Stevensville.
- EMS
- AEP (electric) is on an 800 Mhz analog EDACS system
Also to keep in mind is that during the summer months it is quite common for conditions to be quite good for receiving signals for the Chicago area, so be prepared for that. Sometimes it's nice, and other times you give thanks for PL/CTCSS/DPL tones.
I don't know when you're coming, and maybe you want to keep the specifics to yourself, but try the following site for much information on the area (festivals, things to do, etc.)
Southwestern Michigan Tourist Council
P.S. The place mentioned in New Buffalo is the Stray Dog. I haven't been there, but can recommend Casey's in New Buffalo. Send me a PM if interested in more good places to eat. I can tell you what places my wife and I like.