Are Postnuptial Agreements Valid in Illinois?

Postnuptial agreements—contracts entered into by spouses after marriage to resolve financial and property issues—have grown increasingly common in recent years. While prenuptial agreements are well-known and widely used, many married couples are unaware that they can enter into similar agreements even after the wedding day. You may be wondering, “Are postnuptial agreements valid in Illinois?” The answer is yes, a postnuptial agreement will be upheld and enforced in Illinois courts, so long as certain conditions are met.

Legal Framework for Postnuptial Agreements in Illinois

Illinois does not have a statute specifically governing postnuptial agreements, unlike premarital agreements, which are governed under the Illinois Uniform Premarital Agreement Act (750 ILCS 10/1, et seq.). However, postnuptial agreements are recognized and enforced under general contract law principles and sections of the Illinois Marriage and Dissolution of Marriage Act (“IMDMA”).

Enforceability Standards for Postnups

For a postnuptial agreement to be valid in Illinois, courts require the following:

• Voluntariness: The agreement must be entered into freely and without coercion or duress.
• Full Disclosure: Each spouse must make full and fair disclosure of assets and liabilities.
• Capacity: The parties must have the mental competence to understand and consent to the agreement.
• Fairness: The terms must be substantively fair and not unconscionable at the time of execution or enforcement.
• Public Policy: The agreement must not violate public policy, meaning you cannot include provisions regarding child custody or child support.

Case Study: In re Marriage of Chamberlain

The 2024 case In re Marriage of Chamberlain provides a detailed look at how Illinois courts assess the enforceability of postnuptial agreements. The case involved a long-term marriage, a serious medical crisis, and alleged financial and caregiving misconduct—all of which contributed to the court’s conclusion that the postnuptial agreement was invalid and not enforceable.

The parties in this case were married for approximately 40 years, and Wife filed for divorce in 2011. That same year, Husband moved from Illinois to Texas, where he suffered a debilitating stroke that left him a quadriplegic. He then asked his wife to take him back, and she agreed on the condition that he sign a postnuptial agreement, a quitclaim deed transferring his interest in the marital residence to her, and updated power of attorney documents naming her as his agent.

In return, Wife agreed to dismiss the pending divorce case and care for Husband at home. The postnuptial agreement the parties signed heavily favored Wife. It included statements that both parties signed the postnup voluntarily, with no coercion or mental incapacity. However, Husband did not have his own attorney representing and advising him throughout the postnuptial agreement negotiation process.

Wife later placed a mortgage on the marital residence, signing Husband’s name, and allegedly transferred his disability payments into her personal account without Husband’s knowledge or consent.

By 2021, Husband had moved to a veterans’ facility. Wife refiled for divorce and sought to enforce the postnuptial agreement. The trial court ruled that the agreement was procedurally and substantively unconscionable – basically, that it was unfair. The Court found that Husband was likely not cognitively able to consent to the postnuptial agreement when he signed, and as such, it was signed under duress. The Court awarded Husband 50% of the value of the home he had signed away to Wife, along with other assets from the marital estate. Wife appealed the ruling.

The Illinois Appellate Court affirmed that the postnuptial agreement was not enforceable. It emphasized Husband’s cognitive limitations at the time of signing, the fact that he had no independent legal counsel helping to negotiate the postnup, and Wife’s breach of fiduciary and financial responsibilities. The agreement was held to be both procedurally and substantively unconscionable, meaning that the terms of the agreement were unfair, and that the methods by which Wife tricked Husband into signing the agreement were also unfair.

Mental Capacity and Coercion

The Chamberlain case underscores that mental competency and voluntariness are critical in assessing the enforceability of postnuptial agreements. Husband’s cognitive limitations, combined with the stress of medical dependency and his lack of legal advice, led the court to conclude that he did not validly consent to the terms of the postnuptial agreement.

Legal Counsel Protects Both Parties

The absence of independent legal representation for Husband was a major factor in the court’s analysis, as well. While not strictly required by statute, legal counsel helps establish that each party understands the postnuptial agreement and voluntarily consents to its terms.

An Experienced Family Law Attorney in Chicago Can Help

Postnuptial agreements are valid and enforceable in Illinois—but only if they meet standards of fairness, voluntariness, and legal integrity. Spouses entering into postnuptial agreements should ensure full disclosure of their assets and liabilities, obtain independent legal advice, and avoid any appearance of coercion or undue influence. Without those safeguards, Illinois courts are likely to view such agreements with skepticism—and may strike them down altogether. If you are interested in obtaining a postnuptial agreement, reach out to a skilled postnuptial agreement lawyer at O. Long Law, LLC, for help. You can email advice@olonglaw.com or call 847-379-1779 to schedule a consultation with one of our attorneys.