Most people have no idea this is even on the books. Seriously. But adultery is technically illegal in Illinois. The penalties can include jail time and fines. Let me break down what you actually need to know about these old laws and how they affect people today.
Here’s the thing. While adultery is still a crime in Illinois, almost nobody gets prosecuted for it. The last documented case was back in 1997. That’s over 25 years ago. But the law hasn’t gone anywhere, and it’s worth understanding what it says.
What Is Adultery in Illinois?
Adultery has a specific legal definition in Illinois. It’s not just any kind of cheating.
Under Illinois law (720 ILCS 5/11-35), adultery happens when someone has sexual intercourse with a person who isn’t their spouse. But there’s a catch. The behavior has to be “open and notorious.” This means the affair has to be pretty obvious or public. Sneaking around in secret might not technically count under the law.
The law applies in two situations. First, if you’re married and you know the other person isn’t your spouse. Second, if you’re not married but you know the other person is married. Basically, both parties can be charged if they know someone in the relationship is married.
Not sure what counts as “open and notorious”? Join the club. This vague language is one reason prosecutors rarely touch these cases. It’s hard to prove, and honestly, most don’t want to bother.
Criminal Penalties for Adultery
Wait, it gets serious. Adultery is classified as a Class A misdemeanor in Illinois. That’s the most severe type of misdemeanor you can get.
The maximum penalties include up to 364 days in jail. That’s almost a full year. You could also face a fine up to $2,500. Some people get both jail time and fines.
Pretty harsh for something that’s basically never prosecuted, right?
Class A misdemeanors are no joke. They’re just one step below felony charges. Other Class A misdemeanors include DUI, domestic battery, and assault. So technically, Illinois treats adultery like it’s on the same level as those crimes.
Why Isn’t Anyone Getting Prosecuted?
Here’s where it gets interesting. The law exists, but prosecutors don’t use it.
The last known adultery prosecution in Illinois was in 1997. Even the prosecutors involved in that case were surprised to see the law actually used. Since then, nothing. Zero cases that anyone can document.
Why keep a law that nobody enforces? Good question. Maybe lawmakers don’t want to publicly support removing it. Maybe it’s just more trouble than it’s worth to repeal an old law that’s collecting dust. Nobody really knows.
Think of it like one of those weird old laws you hear about. Technically illegal, but practically forgotten.
How Adultery Affects Divorce in Illinois
Okay, pause. This part is actually important.
Illinois became a no-fault divorce state in 2016. This changed everything about how adultery affects divorce cases. Before 2016, you had to prove your spouse did something wrong to get a divorce. Adultery was one of those grounds.
Now? You don’t need to prove anything. The only legal ground for divorce in Illinois is “irreconcilable differences.” This means the marriage is broken beyond repair. That’s it.
So adultery can’t be used as a reason for divorce anymore. Cheating might be why you want to get divorced, but legally speaking, it’s irrelevant.
Most people expect the cheating spouse to get punished in divorce court. They think proof of an affair will help them get more money or custody. Honestly, that’s not how it works in Illinois.
Does Adultery Affect Property Division?
Short answer? Not directly.
Illinois uses “equitable distribution” when dividing marital property. This means assets get divided fairly, not necessarily equally. The law specifically bars judges from considering marital misconduct when dividing property.
So the affair itself won’t matter. The judge can’t give you more just because your spouse cheated.
But wait, there’s an exception. It’s called dissipation of marital assets. This is where adultery can actually hit your ex’s wallet.
Let’s say your spouse spent thousands of dollars on their affair. Hotel rooms, fancy dinners, gifts, vacations. Maybe they even paid rent for their lover’s apartment. That money came from marital assets. Money that should have been for both of you.
If you can prove this happened, the court might make your spouse reimburse the marital estate. You could get a larger share of the remaining assets to make up for what they wasted. This isn’t punishment for cheating. It’s compensation for financial harm.
You’ll need solid proof though. Bank statements, credit card bills, receipts. The clearer your documentation, the better your case.
Adultery and Child Custody
Here’s where things get tricky. Child custody decisions in Illinois are based on one thing: the best interests of the child.
The affair itself doesn’t automatically affect custody. Just because your spouse cheated on you doesn’t mean they’re a bad parent. Courts separate marital issues from parenting issues.
However. If the adultery directly harmed your children, that’s different. Maybe the affair partner was abusive. Maybe your spouse neglected the kids while pursuing the relationship. Maybe the children were exposed to inappropriate situations.
In these cases, the affair becomes relevant. Not because cheating is wrong, but because it affected the kids. You’d need tangible proof though. Vague claims won’t cut it.
Most of the time, adultery won’t impact custody or visitation rights. The focus stays on the parent-child relationship, not the marriage.
How Adultery Affects Alimony
Illinois law is crystal clear on this one. Judges must make alimony decisions “without regard to marital misconduct.”
That’s straight from the statute (750 ILCS 5/504(a)). Your spouse’s affair cannot be considered when determining spousal maintenance. Period.
The court looks at specific factors instead. Length of the marriage. Each spouse’s income and earning potential. Age and health. Standard of living during the marriage. Contributions each spouse made to the marriage.
Notice what’s missing from that list? Fault. Blame. Cheating. None of it matters for alimony calculations.
Again though, dissipation of assets can come into play. If marital funds were wasted on the affair, that financial misconduct might indirectly affect the final settlement. But you’re addressing the financial harm, not the cheating itself.
Recent Changes to Illinois Divorce Law
Stay with me here. While the no-fault divorce rules haven’t changed, Illinois updated some other divorce-related laws in 2025.
Parenting plans are now considered final orders once approved. This means they’re immediately enforceable and appealable. But if the underlying divorce case gets dismissed, the parenting plan is voided too.
Distance for parental relocation is now measured by the shortest surface-road route. Not straight-line distance. This affects cases where one parent wants to move farther away.
Spousal maintenance for incarcerated payors changed. Courts no longer automatically pause maintenance payments just because the paying spouse is in jail.
These updates don’t directly relate to adultery. But they might affect your overall divorce case.
Can You Sue for Emotional Distress?
Some states used to allow lawsuits for “alienation of affection.” Basically, suing your spouse’s affair partner for stealing your spouse’s love. Illinois had these laws too.
Not anymore. Illinois abolished “heart balm” acts on January 1, 2016. This includes alienation of affection claims. You cannot sue someone for having an affair with your spouse.
You might be able to sue for intentional infliction of emotional distress. But this is extremely difficult to prove. You’d need to show the conduct was outrageous and caused severe emotional harm. Expert testimony from counselors or therapists is usually required.
Honestly, these cases rarely succeed. The emotional and financial cost of pursuing them often isn’t worth it.
Proving Adultery in a Divorce
Even though adultery doesn’t affect the divorce itself, you might still want to prove it. Maybe for dissipation claims. Maybe for peace of mind.
How do you prove it? Carefully.
You can use bank statements, credit card bills, phone records, emails, text messages. Photos or videos might help. Witness testimony from people who saw the affair.
Here’s where people get in trouble. Don’t do anything illegal to gather evidence. Illinois law prohibits recording conversations without consent. You can’t hack into your spouse’s phone or email.
Breaking the law to gather evidence can backfire badly. The evidence might get thrown out. You could face criminal charges yourself.
If you’re thinking about hiring a private investigator, talk to a family law attorney first. They can advise you on what evidence actually helps your case. Private investigators are expensive. The evidence they gather might not even be useful for Illinois divorce proceedings.
What Should You Do If Your Spouse Cheated?
First, take a breath. Discovering infidelity is devastating. Shock, anger, grief. These feelings are completely normal.
Give yourself time to process. Individual therapy can help you work through your emotions and decide what you want to do next.
If you’re considering divorce, talk to a family law attorney. They can explain your options and help you create a divorce plan. In Illinois, many divorces can be resolved without going to court if there are no complex financial issues or parenting disputes.
Some couples choose legal separation instead of divorce. You stay legally married but live separately. This gives time to see if the marriage can be saved. You can always get divorced later if needed.
Others try counseling to repair the relationship. If your spouse genuinely wants to change and you think reconciliation is possible, professional help might work.
There’s no one right answer. You need to decide what’s best for you.
Alternatives to Divorce
Legal separation is an option in Illinois. You remain married but live apart. This works for couples who might reconcile later. It also works for people who want to stay married for religious reasons but need space.
Marriage counseling is another route. If both spouses are willing to work on the relationship, therapy can help. No guarantees, but some marriages survive infidelity.
If you want to remarry someone else eventually, you’ll need a divorce. Legal separation doesn’t allow that.
How to Protect Yourself Financially
Document everything. Save bank statements, credit card bills, tax returns. Make copies before your spouse knows you’re considering divorce.
Open a separate bank account in your name only. Start building a financial cushion. This isn’t about hiding money. It’s about having resources to pay for attorney fees and living expenses.
Check your credit report. Make sure your spouse hasn’t opened accounts in your name or damaged your credit.
If you think your spouse wasted marital funds on an affair, gather proof now. The more evidence you have, the stronger your dissipation claim.
Common Misconceptions About Illinois Adultery Laws
“Adultery will help me in court.” Nope. Not for property division, custody, or alimony. Only for dissipation claims.
“My spouse will go to jail for cheating.” Extremely unlikely. Prosecution is essentially nonexistent.
“I can sue the person my spouse had an affair with.” Not anymore. Illinois abolished these claims in 2016.
“Proving adultery will speed up my divorce.” It won’t. If anything, trying to prove fault can drag things out and cost more.
“A no-fault divorce means I don’t need a lawyer.” False. Even uncontested divorces benefit from legal guidance. There are forms to file, deadlines to meet, and legal requirements to satisfy.
When to Hire an Attorney
If your spouse cheated, you probably need a lawyer. Even if you think the divorce will be simple.
An attorney can tell you whether pursuing a dissipation claim makes sense. They can help you gather proper evidence. They’ll make sure you don’t accidentally do something illegal while investigating.
If there are children involved, legal guidance is crucial. Custody and parenting time decisions affect your kids for years. You want to get it right.
If significant assets are at stake, definitely hire an attorney. Property division can get complicated fast.
Most family law attorneys offer free consultations. Use them. Ask questions. Find someone you trust.
Resources for Help
If you’re going through a divorce, support matters. Consider joining a support group for people dealing with infidelity or divorce.
Individual therapy can help you process your emotions. Some therapists specialize in helping people through divorce.
Financial advisors who work with divorcing clients can help you plan for your financial future.
For legal questions, contact the Illinois State Bar Association. They have a lawyer referral service that can connect you with family law attorneys in your area.
Frequently Asked Questions
Is adultery really illegal in Illinois?
Yes, adultery is technically a Class A misdemeanor under Illinois law. However, it’s almost never prosecuted. The last documented case was in 1997.
Can I go to jail for cheating on my spouse?
Technically yes, but practically no. The maximum penalty is 364 days in jail and a $2,500 fine. But prosecutors don’t pursue these cases anymore.
Will my spouse’s affair help me get more money in the divorce?
Not directly. Illinois is a no-fault state, and judges can’t consider adultery when dividing property or determining alimony. The exception is if your spouse wasted marital money on the affair, which is called dissipation of assets.
Can adultery affect child custody decisions?
Only if the affair directly harmed the children. The affair itself doesn’t matter. What matters is whether it affected your spouse’s parenting or exposed the kids to harmful situations.
What does “open and notorious” mean?
The law requires adultery to be “open and notorious” to be criminal. This means the affair has to be relatively public or obvious. Secret affairs might not meet this standard. This vague language is one reason these laws aren’t enforced.
Can I sue the person my spouse had an affair with?
No. Illinois abolished alienation of affection claims in 2016. You cannot sue someone for having an affair with your spouse.
How do I prove my spouse wasted money on an affair?
Gather bank statements, credit card bills, receipts, and any other financial records showing money spent on the affair. Hotel charges, restaurant bills, gifts, trips. The more documentation you have, the better.
Should I hire a private investigator?
Talk to a family law attorney first. Private investigators are expensive, and the evidence they gather might not help your case in Illinois. An attorney can tell you what evidence actually matters.
What if I want to try to save my marriage?
Consider marriage counseling. If both spouses are willing to work on the relationship, professional help can make a difference. Some marriages do survive infidelity with therapy and effort.
How long does a divorce take in Illinois?
It varies. Uncontested divorces can be finalized in a few months. Contested divorces can take a year or more. Trying to prove fault usually makes the process longer and more expensive.
Final Thoughts
Now you know the basics. Adultery is technically illegal in Illinois, but nobody gets prosecuted for it. It won’t directly affect your divorce, custody, or alimony. The real financial risk is dissipation of marital assets.
If you’re dealing with infidelity, take care of yourself first. Process your emotions. Consider therapy. When you’re ready, talk to a family law attorney about your options.
Don’t make decisions based on anger or revenge. Focus on what you want your future to look like. That’s what really matters.
And remember, you’re not alone. Thousands of people go through this every year in Illinois. There’s help available when you need it.
References
- Illinois Compiled Statutes – 720 ILCS 5/11-35 (Adultery) – Official Illinois criminal statute defining adultery
- Illinois Marriage and Dissolution of Marriage Act – 750 ILCS 5/504 – State law on spousal maintenance and divorce
- Illinois State Bar Association – Family Law Resources – Legal resources and attorney referral services
- Illinois Department of Financial and Professional Regulation – Information on professional services and consumer protection
- American Academy of Matrimonial Lawyers – Illinois Chapter – Resources for finding qualified family law attorneys
