Illinois recognizes a single ground for divorce: irreconcilable differences that have caused the irretrievable breakdown of the marriage. Fault-based grounds like adultery, cruelty, and desertion were eliminated years ago, so you don’t need to prove wrongdoing to end your marriage. What you do need is a 90-day residency tie to the state and either six months of living separate and apart or proof that reconciliation has failed.
The One Statutory Ground
Under 750 ILCS 5/401, a court will dissolve a marriage when it finds that irreconcilable differences have caused an irretrievable breakdown and that past attempts at reconciliation have failed or future attempts would be impractical and not in the family’s best interests.1Illinois General Assembly. 750 ILCS 5/401 – Dissolution of Marriage That is the whole test. There is no menu of fault options, and your petition does not need to describe what your spouse did wrong.
The practical effect is that the threshold question, whether the marriage ends, is rarely where a divorce case gets stuck. The disputes come after: property, support, and parenting.
Two Ways to Establish Irreconcilable Differences
The statute gives you two paths, and the choice affects your timeline.
The Six-Month Separation Presumption
If you and your spouse have lived separate and apart continuously for at least six months immediately before the court enters its judgment, the law creates an irrebuttable presumption that irreconcilable differences exist.1Illinois General Assembly. 750 ILCS 5/401 – Dissolution of Marriage Irrebuttable means your spouse cannot argue against it. Once six months of separation precede the judgment, the ground is proven automatically. No testimony required.
An easy point to miss: the six months must precede entry of judgment, not the filing date. You can file the petition earlier and use the intervening months to work through discovery, property division, and parenting arrangements. The court simply cannot finalize until the six-month mark has passed.
Proving Reconciliation Has Failed
You are not required to wait. If separation hasn’t reached six months, the court can still find irreconcilable differences if you show that reconciliation efforts have failed or that further attempts would be impractical and against the family’s best interests.1Illinois General Assembly. 750 ILCS 5/401 – Dissolution of Marriage This path takes more work because you’re asking the judge to make a finding rather than leaning on a presumption. You’ll need to testify or otherwise put on evidence about why the marriage cannot be saved.
In contested cases, this distinction rarely changes anything. Discovery, negotiation, and court scheduling routinely push a contested divorce past six months on their own. Where the shorter path matters is uncontested cases where both spouses agree and want to finish quickly.
What “Separate and Apart” Means
Living separate and apart does not require two addresses. Spouses who share a household can still qualify for the six-month presumption if they have genuinely stopped functioning as a married couple. This accommodation exists because many families cannot run two households during the transition.
Courts look at the practical reality of daily life. Same-household separation generally means no shared bedroom, no shared meals as a couple, no joint social activities, and no pooling of finances for household management. Splitting groceries and sleeping in different rooms while one spouse waits on a lease can count. Hosting dinner parties together and splitting the cable bill probably will not.
The 90-Day Residency Requirement
Before an Illinois court can hear your case, at least one spouse must have lived in Illinois, or been stationed in the state as a member of the armed services, for at least 90 consecutive days before filing.1Illinois General Assembly. 750 ILCS 5/401 – Dissolution of Marriage Only one spouse needs to meet it. The clock runs backward from the date the petition is filed, not from the date of judgment.
If neither spouse has been in the state long enough when the petition is filed, the court lacks jurisdiction and cannot proceed. The remedy is to wait until the threshold is met and then file.
Where Misconduct Still Matters
People often hear “no-fault” and assume nothing their spouse did will ever come up. That is not quite right. Misconduct cannot block a divorce, but it can still surface in the money and parenting fights that follow.
Property Division and Dissipation
Illinois law directs courts to divide marital property “without regard to marital misconduct,” so an affair by itself will not change how assets are split. Dissipation, however, is a distinct factor the court must weigh. If your spouse drained savings on gambling, spent lavishly on an affair partner, or hid assets during the breakdown of the marriage, you can bring a dissipation claim, and the court will account for those wasted assets in the division.2Illinois General Assembly. 750 ILCS 5/503 – Disposition of Property and Debts A dissipation claim requires formal notice filed at least 60 days before trial, identifying the property and timeframe.
Maintenance
Maintenance is also determined “without regard to marital misconduct.”3Illinois General Assembly. 750 ILCS 5/504 – Maintenance The court looks at income, earning capacity, the standard of living during the marriage, and how long the marriage lasted. Bad behavior will not raise or lower the award.
Parenting Time
Parenting decisions are where misconduct genuinely moves the needle. When allocating parenting time, a court must consider threats of physical violence directed at the child or any household member, any history of abuse, and whether a parent is a convicted sex offender.4Illinois General Assembly. 750 ILCS 5/602.7 – Best Interests of Child Ordinary marital misconduct that does not affect the parent-child relationship, such as infidelity, is not a factor. Conduct involving violence, substance abuse, or criminal behavior that touches the children absolutely is.
Putting It Together
To get divorced in Illinois, one spouse must have 90 days of residency, and you must either wait for the six-month separation presumption or convince the court that reconciliation has failed. That’s the whole grounds question. Everything else the case turns on, from asset division to parenting time, gets decided under separate statutes with their own rules about what the court can and cannot consider.