Republican Mike Bost, a long-time state representative from Carbondale, has defeated incumbent Bill Enyart, a Democrat, in the state's 12th Congressional District.
Enyart, of Belleville, has been voted out after serving only one term. He was first elected in 2012.
According to the Associated Press, Bost has received 55.27 percent of the vote to Enyart's 38.64.
Green Party candidate Paula Bradshaw received 6.09 percent.
"I am humbled beyond words by the trust that the people of Illinois have put in me tonight," Bost said in a statement.
"To the voters of the 12th District - from Alton to Cairo, and back to Mount Vernon - I can only say thank you, and I will do my utmost every day to fight for you in Washington. I thank Congressman Enyart for his service to our country, and look forward to working with him in the transitional months ahead."