I'm thinking that you may want to try Rockford. I've ridden on several MUP's in that town. One runs N-S along the river, another runs North, up to the big state park, connecting to a nice long E-W trail -- by far the best ride. I think there is even a third path that runs south of town to another park on a river (Kishwaukee?).
I do not remember there being anything bike related in Belvidere.