750 ILCS 5/301

Declaration of Invalidity - Grounds.) The court shall enter its judgment declaring the invalidity of a marriage (formerly known as annulment) entered into under the following circumstances:

(1) a party lacked capacity to consent to the marriage at the time the marriage was solemnized, either because of mental incapacity or infirmity or because of the influence of alcohol, drugs or other incapacitating substances, or a party was induced to enter into a marriage by force or duress or by fraud involving the essentials of marriage;

(2) a party lacks the physical capacity to consummate the marriage by sexual intercourse and at the time the marriage was solemnized the other party did not know of the incapacity;

(3) a party was aged 16 or 17 years and did not have the consent of his parents or guardian or judicial approval; or

(4) the marriage is prohibited.