As Illinois House lawmakers prepare to debate a gay marriage bill, a new poll shows support at an all-time high.

According to a Crain's Chicago Business/Ipsos Illinois Poll released Tuesday, most Illinois residents favor passage of the proposed legislation.

Of the 600 adults surveyed, 50 percent said they support the marriage equality bill, while 29 percent said they remain oppose. Another twenty percent said they did not know or had mixed feelings on the subject.

Support is strongest in Chicago, with 56 percent in favor. A majority (52%) of suburban residents also approve. But only 48 percent of those living outside the Chicago metropolitan area support the measure's passage.

A majority (51%) of those opposed cited religious beliefs for opposing marriage equality.

Over the past two-and-a-half years, support has increased from 34 percent in 2010 to 44 percent in September of last year, according to polls by Southern Illinois University's Simon Public Policy Institute.

The measure cleared the Senate last Thursday, Valentine's Day. And House lawmakers are expected to begin debate on Wednesday.

(Related: Illinois House could vote on gay marriage bill this week.)