Your ex can fight your move to Ill. However, it appears that you may have a valid reason for the move. It appears that you are trying to better the life of your child. As long as you are not moving to spite your ex and are amenable to continuing to allow him to have a simialr amount of visitaion time, the court may allow your move.
If your ex is fighting you over the intended move you will need legal representation in this matter.
As a licensed michigan attorney I would be more than glad to discuss representing you in this matter. Email me to set up a free consultation at jrothstein05@gmail.com