Democrat incumbent Rep. Katie Stuart has defeated Republican challenger Jennifer Korte by 2,968 votes - 20,200 to 17,232, according to unofficial totals in Madison and St. Clair counties.
In Madison County, Stuart received 13,588 votes to Korte's 11,735.
In St. Clair County, Stuart had 6,612 votes to Korte's 5,497.
Korte said that she was "thankful for everyone who helped my campaign and for the opportunity to meet thousands of wonderful people while knocking on doors and campaigning for the last year," in a Facebook post.
"I have seen our neighbors' stress when they talk about our future as we deal with rising energy costs, expensive gas, rising grocery prices, and high property taxes.
"I congratulate Katie on her win, but our work does not stop tonight; we must continue to ensure a better, more accountable government that reflects the priorities of our district."
Stuart thanked her supporters.
"It means so much to have the support of friends, family, and so many others," she wrote on Facebook. "I look forward to continuing to work for the 112th district!"
Stuart benefited from a significant funding advantage over Korte, having accepted close to $2 million in contributions this year.