"Father" means a man presumed to be the natural father of a child if:
he and the child's natural mother are or have been married to each other, even though the marriage is or could be declared invalid, and the child is born or conceived during such marriage;
after the child's birth, he and the child's natural mother have married each other, even though the marriage is or could be declared invalid, and he is named, with his consent, as the child's father on the child's birth certificate pursuant to Section 12 of the Vital Records Act;
he and the natural mother have signed an acknowledgment of paternity in accordance with rules adopted by the Illinois Department of Public Aid under Section 10-17.7 of the Illinois Public Aid Code; or
he and the child's mother have signed a petition to establish the parent and child relationship by consent of the parties in accordance with Section 6 of the Act.
A man can rebut a presumption of paternity before a court of jurisdiction [750 ILCS 45/5]. Father also means a man who adopts a child or has been determined by court or administrative adjudication to be the child's father. (R 301, 315)