According to a study by the liberal Williams Institute, legalizing gay marriage in Illinois would generate up to $103 million in spending to the state and local economy.
The Institute argues that same sex marriage creates an "economic boost" through increased wedding ceremonies, tourism, and sales tax revenue, and contends that states with high unemployment and cash-strapped budgets must legalize it in order to ease their financial crisis.
According to the Institute, 23,049 same-sex couples live in Illinois. Of those couples, the Institute estimates that 50% (11,525 couples) would choose to marry in the first three years. Of the couples that will marry, 64% of those marriages will occur during the first year, 21% in the second year and 15% in the third year.
As a result, the study estimates that the state's wedding business would see an increase by $74 million, and an increase of $29 million in tourism by out-of-town guests. They estimate that the increased wedding spending would generate approx. 281 jobs and produce tax revenue of $8.5 million.
The report does not include spending estimates for out-of-state gay couples that might travel to Illinois to marry. It also does not include the significant tax revenue lost as a result of the tax benefits realized by married couples, which are estimated to far outweigh the increased revenue from the "marriage business" spike assumed in the study.
The study can be viewed here http://williamsinstitute.law.ucla.edu/wp-content/uploads/IL-Econ-Impact-Mar-2013.pdf.