Illinois
Illinois Prenuptial Agreement Laws: Enforceability and Limits (2026)
Independently fact-checked against primary sources (last audited October 8, 2026). · 4 primary sources cited on this page. How we verify our legal content
Yes, a prenuptial agreement can be enforceable in Illinois. The Illinois Uniform Premarital Agreement Act, 750 ILCS 10, requires the agreement to be in writing and signed by both parties (Section 3), and Section 7 sets out when a court will refuse to enforce it: an involuntary signature, or an agreement that was unconscionable when signed where the resisting party also lacked fair disclosure and a written waiver of disclosure, and did not have, or reasonably could not have had, adequate knowledge of the other side's finances.
Information last verified on 2026-10-08. This article has not been reviewed by a licensed lawyer.
Jurisdiction scope: This article covers premarital agreements under the Illinois Uniform Premarital Agreement Act, 750 ILCS 10, Sections 1 to 11, with notes on Sections 502 and 503 of 750 ILCS 5. It does not summarize Illinois court decisions applying the Act, other states' prenup laws, or how to draft an agreement. For property division without a prenup, see Illinois divorce laws.
Which Illinois law governs prenups
Illinois prenups are governed by a dedicated statute. Section 1 provides: "This Article shall be known and may be cited as the Illinois Uniform Premarital Agreement Act."
The Act is short, 11 sections in all, and it applies by date. Section 11 states: "This Article applies to any premarital agreement executed on or after January 1, 1990." This page does not cover agreements signed before that date.
Formal requirements for an Illinois prenup
Section 3 sets the basic formalities:
"A premarital agreement must be in writing and signed by both parties. It is enforceable without consideration." 750 ILCS 10/3
The agreement does not take effect at signing. Section 5 states: "A premarital agreement becomes effective upon marriage."
The Act's 11 sections do not require notarization or witnesses.
What an Illinois prenup can cover
Section 4(a) lists the subjects the parties may contract on. They include each party's property rights; how property is disposed of on separation, dissolution, death or another event; the modification or elimination of spousal support; wills and trusts; life insurance proceeds; the choice of law governing the agreement; and any other matter that does not violate public policy or a criminal statute (750 ILCS 10/4(a)).
These agreements are drafted and reviewed by lawyers licensed in Illinois. This page describes the law and does not offer terms to use.
What a prenup cannot do in Illinois
A prenup cannot cut into a child's support. Section 4(b) states: "The right of a child to support may not be adversely affected by a premarital agreement."
When a court will not enforce a prenup
Section 7 places the burden on the party who wants out of the agreement. It gives two routes.
| Challenge | What the resisting party must prove | Cite |
|---|---|---|
| Involuntary signing | That party "did not execute the agreement voluntarily" | 750 ILCS 10/7(a)(1) |
| Unconscionability plus missing disclosure | The agreement was unconscionable when it was executed, and before signing that party (i) was not given a fair and reasonable disclosure of the other's property or financial obligations, (ii) did not voluntarily and expressly waive disclosure in writing, and (iii) did not have, or reasonably could not have had, adequate knowledge of the other's property or financial obligations | 750 ILCS 10/7(a)(2) |
| Who decides unconscionability | The court, as a matter of law | 750 ILCS 10/7(c) |
Unconscionability is tested at signing
The second route looks back to the moment of signing. Section 7(a)(2) asks whether "the agreement was unconscionable when it was executed," not whether it seems unfair years later at divorce. And unconscionability alone is not enough: the resisting party must also prove all three disclosure shortfalls.
Waiving financial disclosure
Disclosure can be waived, but only in a specific way. The waiver must be voluntary, express and in writing. The second disclosure element is met when the resisting party "did not voluntarily and expressly waive, in writing, any right to disclosure of the property or financial obligations of the other party beyond the disclosure provided" (750 ILCS 10/7(a)(2)(ii)).
Spousal support waivers
An Illinois prenup may modify or eliminate spousal support (750 ILCS 10/4(a)). Section 7(b) adds a safety valve. If a support term would cause a party undue hardship because of circumstances not reasonably foreseeable when the agreement was signed, "a court, notwithstanding the terms of the agreement, may require the other party to provide support to the extent necessary to avoid such hardship."
For how maintenance works when there is no enforceable waiver, see Illinois alimony laws.
Lawyers, waiting periods and timing
The Act's 11 sections contain no independent-counsel requirement, no minimum waiting period between presenting and signing the agreement, and no public-assistance bar. A lawyer licensed in Illinois can draft or review these agreements and can explain how the Section 7 tests apply to a particular one.
If the marriage turns out to be void
Section 8 covers the case where the marriage is determined to be void. Then "an agreement that would otherwise have been a premarital agreement is enforceable only to the extent necessary to avoid an inequitable result" (750 ILCS 10/8).
Changing or revoking a prenup after the wedding
Section 6 controls changes after marriage:
"After marriage, a premarital agreement may be amended or revoked only by a written agreement signed by the parties." 750 ILCS 10/6
Like the original agreement, an amendment or revocation is enforceable without consideration (750 ILCS 10/6).
Time limits on prenup claims
Section 9 pauses the clock during the marriage: "Any statute of limitations applicable to an action asserting a claim for relief under a premarital agreement is tolled during the marriage of the parties to the agreement." The same section keeps the equitable defenses of laches and estoppel available (750 ILCS 10/9).
Postnuptial agreements in Illinois
The Illinois Uniform Premarital Agreement Act addresses agreements made before marriage and does not contain a postnuptial agreement provision. Section 502 of 750 ILCS 5 lets spouses make an agreement, generally in writing, on property, maintenance and support attendant upon a dissolution, and it binds the court unless the court finds it unconscionable:
"The terms of the agreement, except those providing for the support and parental responsibility allocation of children, are binding upon the court unless it finds ... that the agreement is unconscionable." 750 ILCS 5/502(b)
That is a divorce settlement agreement rule, not a general postnup statute. This page does not cover Illinois case law on stand-alone postnuptial agreements.
How Illinois divides property without a prenup
Without an agreement, Illinois divides "marital property" in a divorce, which Section 503(a) defines as property "acquired by either spouse subsequent to the marriage," minus listed non-marital categories, and the court divides it in just proportions (750 ILCS 5/503(d)). See Illinois divorce laws for details.
Disclaimer: This article provides general legal information about premarital agreements under the Illinois Uniform Premarital Agreement Act, 750 ILCS 10, verified against the Illinois General Assembly's statute text on 2026-10-08. It is not legal advice and is not a template. For advice about an agreement, consult a lawyer licensed in Illinois.
Related
Last updated: 2026-10-08.
Frequently Asked Questions
Are prenups enforceable in Illinois?
Yes, if they meet the Illinois Uniform Premarital Agreement Act. An agreement in writing signed by both parties is enforceable unless the resisting party proves involuntary signing or unconscionability with the disclosure failures in 750 ILCS 10/7(a).
Does a prenup have to be notarized in Illinois?
The Act does not require it. Section 3 requires only a writing signed by both parties, and none of the Act's 11 sections adds a notarization or witness requirement.
Do both parties need a lawyer for a prenup in Illinois?
The Act's 11 sections contain no independent-counsel requirement. Enforceability turns on the tests in 750 ILCS 10/7: voluntariness, and unconscionability combined with missing disclosure.
Can a prenup waive alimony in Illinois?
Section 4(a) allows a prenup to modify or eliminate spousal support. Under Section 7(b), a court may still order support to the extent needed to avoid undue hardship from circumstances not reasonably foreseeable at signing.
Can a prenup decide child support in Illinois?
No. Under 750 ILCS 10/4(b), a premarital agreement may not adversely affect a child's right to support.
Can you change a prenup after marriage in Illinois?
Yes, but only by a written agreement signed by both spouses, which is enforceable without consideration (750 ILCS 10/6).
When does an Illinois prenup take effect?
On the marriage. Section 5 of the Act states that a premarital agreement becomes effective upon marriage.
Updates
Independently fact-checked against the cited primary sources
The Law Behind This Article
This article rests on the statutory provisions below, held in our own legal record and retrieved from the official source. Tap a section to read the operative text.
Illinois Compiled Statutes Chapter 750, Act 10 (Illinois Uniform Premarital Agreement Act)
§ 7EnforcementIn force
(a) A premarital agreement is not enforceable if the party against whom enforcement is sought proves that: (1) that party did not execute the agreement voluntarily; or (2) the agreement was unconscionable when it was executed and, before execution of the agreement, that party: (i) was not provided a fair and reasonable disclosure of the property or financial obligations of the other party; (ii) did not voluntarily and expressly waive, in writing, any right to disclosure of the property or financial obligations of the other party beyond the disclosure provided; and (iii) did not have, or reasonably could not have had, an adequate knowledge of the property or financial obligations of the other party. (b) If a provision of a premarital agreement modifies or eliminates spousal support and that modification or elimination causes one party to the agreement undue hardship in light of circumstances not reasonably foreseeable at the time of the execution of the agreement, a court, notwithstanding the terms of the agreement, may require the other party to provide support to the extent necessary to avoid such hardship.
Official text (excerpt) · last checked 2026-07-29 · Read the full text in our law library · Verify at ilga.gov
§ 3FormalitiesIn force
A premarital agreement must be in writing and signed by both parties. It is enforceable without consideration.
Official text (excerpt) · last checked 2026-07-29 · Read the full text in our law library · Verify at ilga.gov
§ 4ContentIn force
(a) Parties to a premarital agreement may contract with respect to: (1) the rights and obligations of each of the parties in any of the property of either or both of them whenever and wherever acquired or located; (2) the right to buy, sell, use, transfer, exchange, abandon, lease, consume, expend, assign, create a security interest in, mortgage, encumber, dispose of, or otherwise manage and control property; (3) the disposition of property upon separation, marital dissolution, death, or the occurrence or nonoccurrence of any other event; (4) the modification or elimination of spousal support; (5) the making of a will, trust, or other arrangement to carry out the provisions of the agreement; (6) the ownership rights in and disposition of the death benefit from a life insurance policy; (7) the choice of law governing the construction of the agreement; and (8) any other matter, including their personal rights and obligations, not in violation of public policy or a statute imposing a criminal penalty. (b) The right of a child to support may not be adversely affected by a premarital agreement.
Official text (excerpt) · last checked 2026-07-29 · Read the full text in our law library · Verify at ilga.gov
§ 9Limitation of actionsIn force
Any statute of limitations applicable to an action asserting a claim for relief under a premarital agreement is tolled during the marriage of the parties to the agreement. However, equitable defenses limiting the time for enforcement, including laches and estoppel, are available to either party.
Official text (excerpt) · last checked 2026-07-29 · Read the full text in our law library · Verify at ilga.gov
Illinois Compiled Statutes Chapter 750, Act 5 (Illinois Marriage and Dissolution of Marriage Act)
§ 502AgreementIn force
(a) To promote amicable settlement of disputes between parties to a marriage attendant upon the dissolution of their marriage, the parties may enter into an agreement containing provisions for disposition of any property owned by either of them, maintenance of either of them, support, parental responsibility allocation of their children, and support of their children as provided in Sections 513 and 513.5 after the children attain majority. The parties may also enter into an agreement allocating the sole or joint ownership of or responsibility for a companion animal. As used in this Section, "companion animal" does not include a service animal as defined in Section 2.01c of the Humane Care for Animals Act. Any agreement pursuant to this Section must be in writing, except for good cause shown with the approval of the court, before proceeding to an oral prove up.
Official text (excerpt) · last checked 2026-07-29 · Read the full text in our law library · Verify at ilga.gov
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Sources and References
- Illinois Uniform Premarital Agreement Act, 750 ILCS 10, full text (Sections 1-11)(www.ilga.gov).gov
- Illinois Uniform Premarital Agreement Act, 750 ILCS 10, section listing and text (Illinois General Assembly)(www.ilga.gov).gov
- 750 ILCS 5, Part V (Sections 501-510): settlement agreements (502) and property disposition (503)(www.ilga.gov).gov
- Illinois Compiled Statutes, 750 ILCS 5 (Illinois Marriage and Dissolution of Marriage Act), full text(www.ilga.gov).gov