I want to get a child support order which state is involved?

Having problems with the mother and I just want a mediator to control what I am paying. That way we might have less to argue about. I love my child and have him 2 days a week minimum. We lived in Indiana but when we split up she went to Chicago. It is about 30 min away so it is not too bad. Now which court would it involve? Indiana or Illinois? I have heard court usually asks for 20 percent of income is that true? any advice would be great. Thanks in advance