Republican state senators on Wednesday night passed over Sen. Kyle McCarter of Lebanon and instead kept Sen. Christine Radogno of Lemont as their caucus leader.
McCarter stated on his Twitter account that not enough senators had "the courage" to vote for him.
The 19 GOP senators held a vote Wednesday night in Springfield to choose their leader.
McCarter had been angling for the position, saying the party needed new leadership in the wake of its poor showing in the election Nov. 6.
On his Twitter account early Thursday morning, McCarter stated: "Stepped up to lead & stood by my principles but not enough Rep senators had the courage to break from the Radogno failing status quo."
Ten votes were needed to be elected minority leader. Radogno received 12.
In the election, Democrats gained five seats in the Illinois Senate. Democrats now hold 40 seats in the chamber.
When new senators and representatives are sworn in, Democrats will have a super-majority in both the Senate and House. They also control the governorship, with Democratic Gov. Pat Quinn of Chicago.
McCarter said earlier this week that Republicans have to "do a better job of articulating our message of smaller government and lower taxes, and opportunities for people to be able to go back to work."
He added, "We've got to do a better job of articulating that, not just to our traditional base, but we've got to reach out to women, to young people and to minorities, and give them a reason to vote for us."
Radogno said Republicans did poorly in a lot of places, not just Illinois.
McCarter, a business owner, has been a senator since 2009. Radogno has been a senator since 1997 and is the first female caucus leader in the history of the Illinois General Assembly.