Updated 1/31/11 10:44 p.m.

CHICAGO (CBS) – Illinois Gov. Pat Quinn has signed legislation legalizing civil unions for gay and lesbian couples.

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Hundreds of supporters crowded into the Chicago Cultural Center on Monday afternoon to watch the historic bill-signing.

“Right on the eve of Abraham Lincoln’s 202nd birthday, I think this is really something very, very special,” Quinn said before taking action.

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.

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“I have a gay daughter, and I see this through her eyes, and it’s opened a whole new world to me,” sponsoring state Sen. Dave Koehler, D-Peoria, said.

Opponents of the new law 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.

The bill passed the state House on Nov. 30, and went on to pass the state Senate the following day, after 90 minutes of impassioned debate.

Illinois becomes just the sixth state to recognize civil unions or domestic partnerships. Six states and the District of Columbia recognize gay marriages.

Some proponents of the new Illinois law say the next step is legalizing gay marriage.  That possibility worries the Illinois Catholic Conference.

“No ideology can erase the certainty that marriage exists solely between a man and a woman,” the conference said in a written statement.

Starting in June, couples will go through a process similar to getting a marriage license. They’ll show up at a county clerk’s office and fill out some forms. Then it’ll be a matter of notifying insurance companies and employers and other parties who should know.   

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The Sun-Times Media Wire contributed to this report.