The Illinois Marriage and Dissolution of Marriage Act (750 ILCS 5), Explained

How the Act is organized

The Illinois Marriage and Dissolution of Marriage Act (IMDMA) is found at 750 ILCS 5 and is split into parts. Part III covers declaring a marriage invalid, Part IV covers divorce and legal separation, Part IV-A sets out the joint simplified dissolution procedure, Part V covers property, support and attorney fees, and Part VI covers the allocation of parental responsibilities, the Illinois term for what used to be called custody and visitation.

Section 102 lists the Act's purposes, including promoting amicable settlement, protecting children from conflict and removing marital misconduct from decisions about a divorce. Section 104 says the case is generally heard in the county where either spouse lives.

Sections you are most likely to see

Orders and agreements cite these sections by number. The table shows what each one lets a person ask for.

Dissolution, legal separation and declaration of invalidity

Dissolution of marriage (section 401)

Illinois divorce is based on irreconcilable differences. Under section 401(a), one spouse must have lived in Illinois, or been stationed here in the armed services, for 90 days before the case is filed or before the court makes its finding. If the spouses have lived separate and apart for at least 6 continuous months before the judgment, section 401(a-5) creates an irrebuttable presumption that the irreconcilable differences requirement is met. Section 401(b) says the court cannot enter the judgment until it has dealt with parental responsibilities, child support, maintenance and property, unless the spouses agree to reserve an issue or the court finds that reserving it is appropriate.

Section 403 lists what the verified petition must include. Once the petition is served or the other spouse appears, section 501.1 puts an automatic stay in place that bars both spouses from abusing or harassing each other or the children, and from hiding a child from the other parent.

Temporary relief (section 501)

While the case is pending, either spouse can ask for temporary maintenance or child support, supported by a financial affidavit. A spouse can also ask the court to stop the other from transferring or hiding property, or from taking a child out of the court's jurisdiction for more than 14 days. Section 501(c-1) allows interim attorney fee awards. See our guide to temporary relief in an Illinois divorce.

Legal separation and invalidity

Section 402 lets a spouse who lives apart ask for support and maintenance without ending the marriage. The court cannot divide property in a legal separation unless the spouses agree. A declaration of invalidity (formerly called an annulment) falls under sections 301 and 302, and most of its grounds have short deadlines, such as 90 days after learning of the condition.

Property division and maintenance

Section 503 separates marital property from non-marital property. Property acquired during the marriage is presumed marital. Section 503(a) lists exceptions, such as gifts and inheritances and property acquired before the marriage. A spouse who claims an exception must prove it by clear and convincing evidence. Retirement benefits earned during the marriage are presumed marital under section 503(b)(2). Our post on QDROs and QILDROs explains how those benefits are divided.

The court assigns each spouse's non-marital property to that spouse and divides marital property "in just proportions," which is not always 50/50. Section 503(d) lists the factors, including each spouse's contributions, the length of the marriage, each spouse's economic circumstances and the tax consequences. A claim that the other spouse wasted marital money (dissipation) requires written notice no later than 60 days before trial or 30 days after discovery closes, whichever is later.

Section 504 governs maintenance. The court first decides whether maintenance is appropriate at all. If it is, statutory guidelines set the amount and duration in many cases, based on both spouses' incomes and the length of the marriage. See our guide to Illinois alimony laws for the formula.

Child support

Section 505 sets child support under the income shares guidelines of the Illinois Department of Healthcare and Family Services. A "child" includes anyone under 18 and an 18-year-old still in high school who is not yet 19. Through December 31, 2026, the shared physical care calculation applies when each parent has at least 146 overnights a year. Public Act 104-0733 lowers that threshold to 110 overnights beginning January 1, 2027.

Section 513 lets the court order contribution to college or other post-high school education expenses, and section 513.5 covers support for an adult child with a disability. Our post on when child support ends in Illinois walks through those rules.

Parental responsibilities and relocation

Section 602.5 allocates significant decision-making on education, health, religion and extracurricular activities. Section 602.7 allocates parenting time based on the child's best interests, using factors such as each parent's wishes and the caretaking each parent did in the past 24 months. Both parents are presumed fit, and parenting time may be restricted only on a finding that it would seriously endanger the child.

Under section 602.10, each parent must file a proposed parenting plan within 120 days after the petition is served or filed, unless the court extends the time. The court must order mediation to help parents form a plan unless it finds an impediment to mediation. Section 609.2 requires a parent who plans to relocate with a child to give at least 60 days' written notice and file it with the clerk. For a child who lives in Cook County, a move counts as a relocation if the new home is more than 25 miles away by road, whether in Illinois or out of state. Section 610.5 controls later changes. Our overview of Illinois parenting time and decision-making laws has more.

Attorney fees and post-judgment changes

Section 508(a) lets the court order one party to contribute to the other's attorney fees after considering both parties' finances. Under section 508(b), a party who fails to follow an order without compelling cause or justification must pay the other side's fees for the enforcement case. See our post on making a spouse pay attorney fees.

Section 510 controls changes after judgment. Child support may be changed on a substantial change in circumstances, and only for payments that come due after the other party receives notice of the motion. Maintenance generally ends when either party dies, when the receiving spouse remarries, or when the receiving spouse lives with another person on a resident, continuing conjugal basis, unless a written agreement says otherwise. Property terms cannot be changed unless the judgment can be reopened under Illinois law. Section 511 says enforcement and modification start with a petition filed in the circuit where the judgment was entered or last modified.

How a case under the Act moves through Cook County

1. A spouse files a petition for dissolution of marriage in the Domestic Relations Division of the Circuit Court of Cook County, whose main courthouse is the Richard J. Daley Center. Most civil filings are made through the statewide e-filing system. Our guide to the petition for dissolution of marriage covers what it contains.
2. The other spouse is served or files an appearance, and the section 501.1 stay takes effect.
3. Either side may file temporary motions and must exchange financial affidavits and supporting documents.
4. If children are involved, Illinois Supreme Court Rule 923 calls for an initial case management conference within 90 days after service, parents complete a parenting education program, and disputed parenting issues go to mediation.
5. The case ends with a written settlement approved under section 502 or with a trial. After proofs close, section 413 says the judgment should be entered within 60 days, or 90 days if the court finds good cause.

Bring any papers you were served, recent pay stubs and tax returns, account and retirement statements, a list of debts and, if you have children, a caretaking calendar.

Common mistakes

• Assuming marital misconduct changes the property split. Sections 503(d) and 504(a) direct the court to decide property and maintenance without regard to marital misconduct.
• Missing the dissipation notice deadline in section 503(d)(2).
• Treating legal separation as a way to divide property without an agreement.
• Stopping or reducing support on your own. A court order controls until it is changed, and section 510 limits changes to payments due after notice.
• Missing the 120-day parenting plan deadline in section 602.10.

Expect the other spouse to respond, seek discovery and propose a different parenting plan.

How Chicago Family Attorneys can help

• Explain which sections of 750 ILCS 5 apply to your situation.
• Prepare petitions, responses, financial affidavits and temporary relief motions.
• Negotiate and draft marital settlement agreements, parenting plans and allocation judgments.
• Represent you at hearings and trial in Cook, DuPage, Will and Lake Counties.
• Offer limited scope help: document drafting from $500 or one hearing appearance from $1,200.

Full representation starts with an initial payment of $1,500 to $2,500, then $500 to $650 per month beginning 30 days after the initial payment while representation remains active. An uncontested divorce is a $1,500 flat fee, and court filing fees are not included. See fees and payment options and the contested divorce cost page, or learn more about our Chicago divorce services.

This article is general information about Illinois law, not legal advice for your situation, and it does not predict the outcome of any case.