You can pack up and move but that will almost certainly trigger a re-working of the parenting schedule and can also be grounds to re-open the custody case (seeking a modification of custody). It's not necessarily a simple thing. I know you've considered all this but the relocation removes the child from school, friends, family, social networks, activities, etc., and that can weigh heavily for a court in some cases.
You're right about one thing: you need advice. Hire an attorney.
As the custodial parent our legislature has given you the sole and full right to move anywhere within the boundaries of the state of Illinois. It is not for anyone to tell you, advise you, or suggest otherwise including lawyers. Your moves is your owm personal business and choice. You do not have to feel bad about it or be chastised into changing your mind. Most likely moving closer to work will benefit your daughter since you should have more time with her and for her. You should check your divorce papers just to be sure there is no mention with regards to moving. Depending on the age of your daughter you can always take her to counseling to help with any adjustment anxiety she might get as a result of the move. Your ex can file to modify visitation due to the move I suggest you two agree to mediate that subject instead of running up legal fees. Good luck!
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