If you go south and west from Backus, before too long you will be in farm country. I would suggest going east into the lakes/woods area, tons of camping there and on into Wisconsin. From there you can drop south to I-94 and then take I-90/I-39 straight south from Madison, bypassing Chicago.
Or better yet, if you have the time follow the Mississippi for a while, some very scenic roads along there.
https://www.dnr.state.mn.us/camping/index.html