Marriage is the legal union of a man and a woman as husband and wife. The legal union conveys rights and privileges on both parties, which are determined by state law.
Requirements. A man and a woman may marry in Illinois if the following conditions are met:
1. if they are at least 16 years old but are not yet 18, men and women may marry with the consent of both parties' parents or guardians, or with judicial permission;
2. if they are at least 18 years old, both are unmarried, and both are of sound mind, they may marry without anyone else's permission.
Procedure. Marriage in Illinois requires two steps. The first is to get a marriage license, which can be obtained from the clerk of court in any Illinois county. The parties fill out a document and pay a fee. Both parties will need to bring birth certificates to prove that they are at least 18. Additional documentation may be required, such as a divorce decree if either party has been married before.
The second step is to exchange vows before an official authorized to formalize vows and at least two witnesses. Vows can be exchanged before either a licensed religious official, such as a priest, minister, or rabbi, or a licensed civic official, such as a court clerk or a judge. Bring your marriage license to the ceremony with you. The official who presided over the ceremony will sign it and forward it on to the clerk, who will register it in the county marriage records.
Common law marriages. Illinois does not recognize common law marriages. A common law marriage is one in which both parties treat themselves as married and hold themselves out as married, by living together and perhaps by raising children together, but they have not been officially married. In those states where common law marriages are recognized, parties who live together can acquire rights just as if they were married, if certain conditions are met.
Prohibited unions. The following types of marriages are prohibited in Illinois: 1. between people who are already married;
2. between ancestor and descendant;
3. between brother and sister (even if adopted);
4. between aunt and nephew or uncle and niece;
5. between first cousins, unless both are at least 50 years old or one of them is permanently sterile.

Gay marriage. Marriages between people of the same sex are not recognized in Illinois.