CHICAGO — The road to Midwestern acceptance of same-sex marriage runs through Illinois, the home of President Obama that is poised to be the 10th state and the first Legislature in the region to endorse such unions.
In a few short years, attitudes about same-sex marriage are changing in the industrial Midwest. Iowa voters ousted three Supreme Court justices in 2010 who backed a unanimous ruling supporting gay marriage a year earlier. However, last November a fourth judge who was part of that decision survived a recall effort. In Minnesota, voters rejected a constitutional amendment that would have limited marriage to a man and a woman.
Then on Thursday — Valentine’s Day — 33 Democrats and one Republican in the Illinois Senate passed and sent to the House of Representatives a gay marriage bill, affirming the growing support for same-sex unions reflected in opinion polls less than a decade after many banned the practice.
‘‘It’s been legalized in several states, and the world didn’t end, so a lot of the fears have been ameliorated,’’ said John Green, a University of Akron political scientist who specializes in religion and politics. ‘‘That doesn’t mean people are happy about it, but the issue doesn’t produce the same negative impact it did several years ago.’’
Passage in Illinois could spur movements in other states, Green said. In Ohio, an effort begun by groups including FreedomOhio is gathering the signatures needed to put a measure repealing the 2004 constitutional amendment banning gay marriage on the statewide ballot as soon as November.
The groups staged a rally Thursday outside the Franklin County Courthouse in Columbus, where couples obtain marriage licenses, to collect signatures and advocate for repeal.
In November, voters in Washington, Maryland, and Maine approved same-sex marriage. The ballot-box success spurred the movement in Illinois, which legalized civil unions between same-sex couples in 2011.
Thursday’s 34-to-21 Senate vote sending the bill to the House occurred as voter support appears to be growing in Illinois. A poll by the Paul Simon Public Policy Institute at Southern Illinois University in Carbondale showed 45 percent of those surveyed back gay marriage, up from 34 percent in 2010. At the same time, opposition dropped to 20 percent from 26 percent. Pollsters spoke with 600 registered voters Jan. 27-Feb. 8.
The Senate debate was often emotional, revolving around biblical references, analogies to breaking down discriminatory barriers, and warnings of societal chaos. State Senator Kyle McCarter, Republican of Lebanon, said lawmakers ‘‘might as well repeal the law of gravity’’ if it’s going to legalize gay marriage. Other opponents called the bill an attack on religious freedom.
‘‘We are knocking down one of the basic foundations of society,’’ said state Senator Tim Bivins, a Republican from Dixon. ‘‘From the Old Testament to the New, there is nothing to support gay marriage.’’
State Senator Kwame Raoul, a Democrat who filled President Obama’s old seat representing Chicago’s South Side, said fears of destroying society’s pillars are unfounded. He said allowing gay marriage is consistent with the nation’s removal of discriminatory laws.
‘‘Let’s knock down this wall because it’s the right thing to do,’’ Raoul said from the Senate floor. ‘‘The sky is not falling, Chicken Little.’’
Obama and other top Democrats have endorsed the measure, while Governor Pat Quinn of Illinois has promised to sign the bill into law. Republicans are split. Pat Brady, state party chairman, supported the measure.
The sole Republican vote in favor came from state Senator Jason Barickman of Bloomington, who said he believes in freedom and that ‘‘this is the right thing to do.’’
Changing public attitudes are driven by younger voters and represent a challenge for Barickman’s party, said David Yepsen, director of the Paul Simon Institute. ‘‘This has been such a rapid transformation,’’ he said, resembling in some ways shifts from support to opposition to the Vietnam War.
Thirty states have constitutional amendments defining marriage as between a man and a woman. Before November, legalization had come solely through legislative or judicial action as gay marriage was defeated all 32 times it appeared on a ballot. Lawmakers in Delaware, Hawaii, Minnesota, New Jersey, and Rhode Island plan to consider or revisit the issue this year.
Backing for gay marriage in the Illinois House isn’t considered as strong as the Senate, though prospects for passage there ‘‘are very good,’’ said Representative Gregory Harris, a Chicago Democrat who is leading the effort in the chamber.
‘‘There is a movement in all segments of our society to do the right and just thing and treat all people equally in the eyes of the law,’’ Harris said during a news briefing after the Senate vote.