Illinois State Senator Sam McCann, who has been in the Senate since 2010, may run for re-election this year as an independent. See this story. In his previous elections he was the Republican nominee. However, this year, he did not file for re-election in the Republican primary, which is being held March 20.
If he does petition as an independent, his only opponent will be only person who did file in the Republican primary. No Democrat is running. Thanks to Sam Cahnman for the link.