A Wisconsin CCW permit isn’t valid in Illinois, but is an Illinois CCW permit valid in Wisconsin? Absolutely. This is one of the issues of reciprocity; it doesn’t always make complete sense.
A Wisconsinite with a CCW permit is only allowed to carry concealed in their vehicle while driving through Illinois. An Illinois CCW permit holder, on the other hand, can carry anywhere in Wisconsin that a Wisconsinite with a CCW permit can.
Illinois, generally speaking, has much more restrictive firearms laws. The training a Wisconsinite receives wouldn’t necessarily prepare him to carry in Illinois. The reverse, however, is also technically true – those in Wisconsin have much more legal freedom than those in Illinois and an Illinois CCW class doesn’t prepare someone from Illinois to carry in Wisconsin.