Is cheating on your spouse illegal in Illinois?

ST. LOUIS – Two weeks after a viral incident at a Coldplay concert sparked speculation about a high-profile affair, there has been renewed public dialogue around the concept of cheating and, legally speaking, how it’s treated under state laws across the United States.

Adultery, a term typically defined as cheating or infidelity through sexual relations, is one of the most commonly cited reasons for divorce in the United States. A 2024 Forbes Advisor-commissioned survey

of 1,000 divorced Americans found that nearly one in three noted adultery was a contributing factor.

In some cases, adultery can be more than just a moral or marital issue, it can carry legal consequences, possibly even grounds for jail time. While there is no federal law banning adultery, laws vary from state to state and could also depend on context.

With that in mind, it bears the question, is cheating on your spouse illegal in Missouri and Illinois? Here’s what FOX 2 found out:

Missouri

Missouri has two laws that indirectly address adultery. One law outlines how Missouri courts determine whether a marriage is “irretrievably broken,” a necessary finding before the state can grant a divorce. If both spouses agree the marriage is over, the court will typically grant the divorce without much further inquiry. However, if one spouse contests it, the court may dig deeper, and adultery can be cited as a reason it is found intolerable to continue the marriage.

Another law affects inheritance. If a surviving spouse “continuously lived” in a state of adultery or abandoned their spouse to be with someone else, they may be disqualified from receiving inheritance, unless the couple reconciled before the death.

That said, Missouri does not have a law that explicitly labels adultery as a criminal offense.

Short answer: No, cheating on your spouse is not illegal in Missouri.

Illinois

Illinois became no-fault divorce state in 2016, eliminating the need for a spouse to prove specific misconduct, such as adultery, to obtain a divorce. Instead, the only legal ground is “irreconcilable differences,” meaning the marriage has broken down beyond repair and reconciliation is not possible, as determined by a judge.

That said, adultery could technically be classified as a crime in Illinois. Under Illinois Statute 720 ILCS 5/11-35, adultery with someone other than your spouse “if the behavior is open and notorious” can be classified as a Class A misdemeanor. If convicted, such an offense could lead to up to one year in jail and $2,500 in fines.

With that in mind, prosecutions for adultery are extremely rare with the last documented case coming in 1997, according to Sterling Lawyers LLC. That’s partially because in modern court proceedings, adultery is more likely to surface as a factor in unrelated legal matters, such as child custody disputes or assets, rather than a standalone criminal offense.

Short answer: Yes, in certain (but rare) cases, cheating on your spouse can be deemed illegal in Illinois.

If you’re involved in a situation where adultery is relevant, whether in divorce proceedings or over other related legal matters, it’s best to consult a qualified family law or criminal law attorney for specific guidance.