What can I do if my girlfriend took my child out of state without my knowledge 6 months ago and now she moved him to another state again?

You should have, and probably still could file a paternity action to establish your parental rights with respect to the child, including timesharing, parental responsibility, child support, etc., and may be able to address the relocation of the child as well. Consult with an attorney to discuss the specifics of your situation and your options.

Then IL no longer has the power to rule on the child's residence. You need to go to the state where the children live.

You just missed the cut off date of 6 months. Now the other state is the home state of the child, and you would have to sue her there.