In the state of Illinois, I have never had a child support order. I have paid child support faithfully over the years and my daughter will be 18 and graduated in May. Can my ex (never married) file a child support order on me now? Can I be forced to pay back child support even though there was never an order? Am I required to pay support now that she will be attending college?

Thanks in advance.

Yes she can file a child support order now. If you have not been paying 20 percent of your net income then you have not been paying enough. And you will have to prove your payments were support not gifts. You need to hire an attorney to represent you now.

Your daughter's mother would not "file a child support order". She would apply for such an order (or "file for" it), asking a judge to enter one.

If she does, in most states child support is not ordered retroactively. She would only be entitled to child support from the date she applied for it. And in most states, child support would not continue after the child reaches age 18.

If she does apply for a child support order, you should oppose her application on the basis that

you have paid her voluntarilly;
retroactive child support is not warranted (depends on Illinois law); and
child support should not be awarded after the child turns 18 (again, depends on Illinois law).