Jason Plummer, the GOP nominee for the 12th U.S. House District seat, conceded defeat to Democratic rival Bill Enyart, who won by nearly 9 percentage points.
Plummer's campaign issued a written statement Wednesday afternoon acknowledging his loss and thanking his supporters.
"I would like to thank the thousands of supporters, volunteers, and friends who backed our campaign," Plummer wrote. "The 12th Congressional District has been a Democratic district for more than 70 years, and we are proud of our campaign and the ideas we articulated and hope that Southern Illinoisans can work together to solve the serious problems facing the region."
In Tuesday night's election, Enyart garnered 154,621 votes out of 299,950 ballots cast, for 51.5 percent of the vote. Plummer received 128,582, for 42.8 percent, while Green Party candidate Paula Bradshaw received 16,747 votes, for about 5.7 percent.
Enyart, 63, a Belleville lawyer and retired commander of the Illinois National Guard, squared off against Plummer, a Fairview Heights developer and vice president of his father's development firm, and Bradshaw, 59, a Carbondale hospital emergency room nurse.
The three candidates had sought to replace U.S. Rep. Jerry Costello, D-Belleville, who retires in January after 24 years in office.
The dozen counties in the 12th U.S. House District stretched south from Alton in Madison County to Cairo in Alexander County, in the state's southernmost tip.