Illinois Gov. Pat Quinn has signed a bill legalizing civil unions for gay and lesbian couples.
Hundreds of supporters crowded into the Chicago Cultural Center on Monday afternoon to watch the historic bill-signing.
The measure gives gay and lesbian couples official recognition from the state and many of the rights that accompany traditional marriage.
That includes the power to decide medical treatment for an ailing partner and the right to inherit a partner's property.
The law will take effect on June 1.
Supporters say civil unions are a matter of basic fairness for all Illinois residents. But opponents argue it threatens the sanctity of marriage and moves Illinois closer to legalizing same-sex marriages.
Illinois law will continue to define marriage as between one man and one woman.