Rep. Eric Turner, R-Cicero, has defeated his opponent but by a smaller margin than originally expected.
The AP reports Turner has received 59 percent of the vote compared to Parvin Gillim's 41 percent.
Turner authored House Joint Resolution 3, the proposed constitutional amendment to define marriage as between a man and a woman.
Recent allegations that Turner violated House Ethics Committee rules likely hurt his campaign.
Turner lobbied against a nursing home construction moratorium, even though he and his son both have ties to the industry.
The House Ethics Committee ultimately cleared Turner of the allegations but also indicated it needed to change its rules to prevent conflicts of interest.