but first he has to be legally determined to be the father. i assume he did not sign the voluntary acknowledgment of paternity, hence the dna test.
until he signs the vap or has a court order of parentage, he is not legally he dad and cannot file for custody as the child is now living with its presumed custodian--mom.
if he does file, it would be not in the probate court since no one is dead and since one need not file for guardianship of ones own son.
i appreciate that you recommended me. but you do not know illinois parentage law and your answer is of no help to the asker.
Thank you for the constructive criticisim and take good care of yourself. regards