You can marry your cousin in Illinois, but only a first cousin who meets one of two conditions: both of you are at least 50 years old, or one of you provides a physician’s certificate confirming permanent and irreversible sterility. Without one of those, the marriage is prohibited under state law, and the consequences reach beyond the marriage simply not being recognized.
The Two Conditions That Make It Legal
Section 212 of the Illinois Marriage and Dissolution of Marriage Act lists first cousin marriage as prohibited, then carves out two exceptions:
- Both parties have reached age 50 at the time of the marriage. No additional paperwork beyond the standard license requirements is needed.
- Either party is permanently and irreversibly sterile, documented by a certificate signed by a licensed physician. Age doesn’t matter under this route.
A general note from a doctor won’t satisfy the second exception. The certificate has to state specifically that the party is permanently and irreversibly sterile, and it must be filed with the county clerk in the county where the marriage will take place at the time you apply for the license.1Justia Law. Illinois Code 750 ILCS 5 Part II – Marriage
What the County Clerk Will Ask For
The Illinois marriage license application asks whether the two applicants are related and, if so, how. Both parties have to appear in person before the county clerk, sign the application, and pay the fee. The clerk issues the license only after receiving proof that the marriage is not prohibited.1Justia Law. Illinois Code 750 ILCS 5 Part II – Marriage
For first cousins relying on age, that means identification showing both are 50 or older. For couples relying on sterility, it means the physician’s certificate at the moment of application. The clerk files the certificate with the application. It isn’t something you can bring back later.
After the license is issued, a one-day waiting period applies before the marriage can be solemnized, unless a court waives it. The license is valid for 60 days in the county that issued it.
What Happens If You Marry Without Meeting Either Condition
If first cousins marry in Illinois without qualifying under the age or sterility exception, the marriage is prohibited and subject to a court declaration of invalidity. Illinois uses that term in place of the older word “annulment.” The marriage doesn’t dissolve automatically; a court has to formally declare it invalid, and once that declaration is entered the law treats the marriage as if it never existed.2Illinois General Assembly. Illinois Code 750 ILCS 5-301 – Declaration of Invalidity
Who can bring that action is broader than most people expect. Either spouse, the State’s Attorney, or a child of either spouse can petition for the declaration. During the parties’ lifetimes there’s no filing deadline. After one spouse dies, the window closes three years from the date of death.
The practical fallout is where couples tend to get hurt. Property rights, inheritance claims, spousal benefits, joint tax filings, and insurance coverage tied to a valid marriage can all come apart when the underlying marriage is declared invalid.
Criminal Penalties
Entering into a prohibited marriage in Illinois is also a Class B misdemeanor. Section 215 of the Act criminalizes violations of the marriage licensing provisions unless another statute sets a different penalty.3Justia Law. Illinois Code 750 ILCS 5 Part II – Marriage A Class B misdemeanor can carry up to six months in jail and a fine of up to $1,500. Prosecutions are rare, but a conviction leaves a permanent criminal record.
Getting Married in Another State Doesn’t Fix It
Illinois residents sometimes ask whether they can travel to a state with no cousin marriage restrictions, get married there, and come home married. Section 216 of the Act answers that directly. If you live in Illinois and intend to keep living here, a marriage performed elsewhere that would be prohibited under Illinois law is void in Illinois, with the same effect as if you had married in-state.3Justia Law. Illinois Code 750 ILCS 5 Part II – Marriage
The evasion rule is unusually broad. It doesn’t merely leave the marriage unrecognized; it treats it as void for all purposes in Illinois. No spousal rights, no inheritance protection, no access to benefits that depend on a valid marriage. The rule turns on residency and intent. If you’re an Illinois resident planning to keep living in Illinois, a wedding in another state won’t produce a legally recognized union once you’re back.
When a Prohibited Marriage Can Become Valid Later
The statute has one relief valve. If the legal impediment is later removed, and the couple continues living together after that point, they’re considered lawfully married as of the date the impediment ended.1Justia Law. Illinois Code 750 ILCS 5 Part II – Marriage For first cousins, that most often means both spouses eventually turning 50. If the couple is still cohabiting when that happens, the marriage becomes valid from that date forward.
Second Cousins and More Distant Relations
The restrictions apply only to first cousins, meaning people who share a set of grandparents. Illinois places no limits on marriage between second cousins, cousins once removed, or any more distant relation. If your relationship is anything more distant than first cousin, none of the age or sterility rules above apply to you.