4-6 hours from Il, I'd recommend Black River falls because it's the closest fun place but it's dusty and smooth with limited mud or really off road. You'll probably put on 60-80 miles in a good day without hitting the same route twice
Oconto county is probably a bit further but the trails are nice. There's deep sand, rolling hills and great food. Easy to hit 100 miles in a day but you'll back track over a few sections of trail
Dunbar is really far, nearly Michigan or into michigan if you like to ride a lot. Fewer stopping points along the trail but again wooded, trails, rolling hills, mud rocks and sand. Always a good time. Definitely enough trails to ride for a weekend and not ride the same trail twice.
Ill report back in a month when I go to the Hurley area and ride the dead horse trail.
Additionally if you want to drive 7 hours the UP has hundreds of miles of trails and lodging to do a multi-day trip