According to the Daily Caller a recent poll of 629 registered voters has Obama under 50% in Cook County, Illinois. 

A poll conducted by Illinois-based pollster and political strategist Michael McKeon found Obama leading Republican Mitt Romney by 49 percent to 37 percent in Cook County, the home of Chicago. That puts him ahead by a far thinner margin than expected in a county he should be winning handsomely.

In the 2010 statewide elections Republicans won almost every other county in Illinois.  Only the vote from Chicago itself  kept the statehouse in Democrat hands.  Quinn had a largely undeserved reputation as a reformers, which helped him prevail.  Republican Mark Kirk beat Obama's minion Alexi Giannoulias for the US Senate Seat in part because many voters couldn't stomach Giannoulias's reputation for corruption.  

If the McKeon poll is accurate Illinois could become a close race because Obama's lead in the city of Chicago is less than overwhelming, with a huge number of undecideds.

In the city of Chicago itself, he retains a 60-29 lead over Romney. But the Republican challenger leads 45-38 in the surrounding areas. Across the county as a whole, Romney leads 43-31 among independent voters, a crucial voting bloc. Romney also holds a 44-38 lead among male voters, and a 53-40 lead among white voters.

These number makes some sense to me.  Obama is largely a creation of the national media. Before his 2004 Democratic National Convention speech he was a largely undistinguished state senator.  He is respected by his base, to be sure, but he isn't loved the way many other politicians have been loved.    For a while now I have been watching the Obama administration with a sinking feeling that I was seeing a replay of the tumultuous years under Mayor Harold Washington when a coalition of black and white progressives ran Chicago and everything from fixing potholes to filling vacant city jobs seemed to be about race.   While progressives still consider that a golden age for Chicago, the fact is a great many voters of all races didn't like what happened during those years.  The first election after Washington's death saw the election of Richard M. Daley.  Over the next 20 years Daley handily beat back progressive challengers such as Judge  R. Eugene "Lynch 'em" Pincham,(1)  Congressman Bobby Rush and Congressman Jesse Jackson, Jr.  Nor was former Senator Carol Moseley Braun able to do much against Daley's chosen successor Rahm Emanuel.  Chicago voters may not be overly concerned about honesty but they have a record of preferring their executives to be competent administrators. 

(1) During the 1987 mayoral election Illinois Appellate court Judge Pincham declared anyone living south of Madison Street "who doesn't cast a vote for Harold Washington ought to be hung."  In Chicago political circles the injudicious judge was for ever after known as "Lynch 'em Pincham".