A case brought by Lambda Legal and the ACLU is pending before a Cook County Circuit Court. It challenges the state's ban on same-sex marriage as unconstitutional. Couples in Illinois are now allowed civil unions.
The poll found that 32% of respondents said they supported civil unions as the right law.
Rep. Greg Harris led the effort to allow civil unions but told the Associated Press that although the poll results are "monumental," he will wait to propose a marriage equality bill until it looks like the votes in the legislature are there.
The poll surveyed 1,261 registered voters from September 4 through September 10.