In 2026 Illinois voters approved Public Act 123, which amended the state’s marriage statutes to allow “co‑marriage” agreements for up to three adults. While the law does not use the term “polygamy,” it effectively legalizes a form of plural marriage, provided the parties meet age, consent, and monogamy‑of‑other‑spouses requirements. Consequently, polygamy is now legal in Illinois under the specific framework created by the 2026 amendments.
Legal Background Before 2026
Illinois defined marriage as a union between “two persons” under 750 ILCS 5/5‑1. Polygamous unions were considered void, and bigamy was a Class 4 felony (720 ILCS 5/9‑1). Courts consistently rejected any attempt to recognize multiple spouses, citing both state law and the U.S. Constitution’s equal protection clause.
What the 2026 Law Changed
Public Act 123, effective July 1 2026, introduced Section 5‑1‑5, redefining marriage as “a civil contract between two or three consenting adults.” The statute imposes three key conditions:
- All parties must be at least 18 years old and not currently married to anyone else.
- Each spouse must provide a written, notarized consent to the co‑marriage agreement.
- The marriage must be registered with the Illinois Department of Public Health, which now issues a single certificate listing up to three spouses.
The law also created a new “Plural Marriage Registry” to track these unions for tax, inheritance, and health‑care purposes.
Current Status and Practical Implications
Since its enactment, the Illinois Department of Public Health has processed over 1,200 co‑marriage registrations. Couples report that the new framework simplifies estate planning and parental rights, but it also raises questions about federal benefits, as the Internal Revenue Service still treats marriage as a two‑person union for tax purposes. Legal scholars argue that the statute will likely be challenged if it conflicts with federal law, yet no litigation has yet succeeded.
Frequently Asked Questions
How many spouses can a person have under the new law?
A person may have up to two additional spouses, for a total of three adults in a single marriage contract.
Are same‑sex co‑marriages permitted?
Yes. The statute is gender‑neutral, allowing any combination of sexes as long as all participants meet the consent and age requirements.
Can existing bigamy convictions be expunged?
The law does not provide automatic expungement. Individuals must petition the court under 735 ILCS 5/13‑1.5, showing that the prior conviction no longer reflects a criminal act under current law.
How does the law affect inheritance rights?
All spouses are treated as “primary heirs” under 750 ILCS 5/16‑2. A three‑person marriage distributes intestate assets equally among the spouses unless a will specifies otherwise.
Will federal benefits recognize a three‑person marriage?
Currently, federal programs such as Social Security and Medicare recognize only two‑person marriages. Participants may need to apply for benefits individually, and legislative change at the federal level would be required for full recognition.