The seat is the one formerly held by President Obama.

Kirk is tied at 41 percent with state Treasurer Alexi Giannoulias with 4 percent preferring some other candidate and 13 percent undecided. He leads Chicago Urban League President Cheryle Jackson by 43 percent to 39 percent with 4 percent preferring someone else and 13 percent undecided. The margin of error is 4.5 points.

A third Democrat, former federal prosecutor David Hoffman trails Kirk. Kirk polls 43 percent to Hoffman's 33 percent with 8 percent preferring someone else and 16 percent undecided.

Giannoulias is considered the frontrunner for the Democratic nomination and has far outpaced his rivals in raising money.