Besides hitting the Level B "enter at your own risk" maintenance roads (which if it rains allot can be come a handful) around here, the only place I can think of to off road is at 600 Acres which is not far from Cedar Rapids. 600 Acres is about 1-2 miles north of Solon Iowa.
Your next option would be to become friends with a farmer that owns some timber areas.
I'm going to start keeping my eyes open for areas to off road legally at. I'll let any that is interested in on what I find.