(750 ILCS 75/25)
Sec. 25. Prohibited civil unions. The following civil unions are prohibited: (1) a civil union entered into prior to both parties attaining 18 years of age; (2) a civil union entered into prior to the dissolution of a marriage or civil union or substantially similar legal relationship of one of the parties; (3) a civil union between an ancestor and a descendant or between siblings whether the relationship is by the half or the whole blood or by adoption; (4) a civil union between an aunt or uncle and a niece or nephew, whether the relationship is by the half or the whole blood or by adoption; and (5) a civil union between first cousins.
(Source: P.A. 98-756, eff. 7-16-14.)