For the latest election results for the Illinois Primary CLICK HERE. . .
Turnout was light in the Chicago area but heavier in Republican strongholds, where voters went to the polls knowing they would play an important role in the battle between Mitt Romney and Rick Santorum for the GOP presidential nomination. The state's primaries come so late on the election calendar that the November presidential field is often settled before Illinois votes.
Catherine Lopez, a homemaker from the Chicago suburb of Winnetka, said she voted for Romney because she thinks he would be most capable of defeating President Barack Obama.
"OK, maybe he's not charismatic," Lopez said of Romney. "But we've had enough charisma with Obama. We need competence."
It was a sentiment shared by Richard Zellers, a retired Kraft foods worker, who was at his polling station in the central Illinois community of St. Joseph early for one reason: "To get President Obama out."
"If a frog was running against Obama, I'd vote for the frog," said Zellers, who along with his wife, Kay, voted for Santorum.
Some voted for candidates who weren't their top choice.
Wheaton resident Jerry Bulifant, 70, voted for Romney because "he's just more electable," he said. "I voted with my conscience. My heart was with Newt Gingrich .... I do think that he would do well in the debates with the president, but with some of his past baggage, it would be a little difficult for him."
According to an exit poll conducted for The Associated Press by Edison Research, four out of 10 Illinois primary voters listed the ability to beat Obama as the top factor in their decision. About a quarter said it was more important to choose a candidate with strong moral character.
A Romney loss in Illinois would all but destroy his battered image as the party's inevitable nominee, while a Santorum loss would deepen doubts about whether he can win any but the most conservative states.
Still, the exit poll showed little sign of primary fatigue. Less than a third of those voting said they hoped the primary season would come to a quick end even if that meant their candidate might lose the nomination. Most voters preferred to see the primaries continue in hopes that their favored candidate would win in the end.
A majority of voters listed the economy as their top voting issue, according to the exit poll.
The day began with ballot problems in nearly a quarter of Illinois counties. Some ballots were too large to fit into scanning machines in 24 counties and the city of Aurora.
Election officials said all votes would be counted despite the mix-up, although the tally could take longer in the affected counties, said Jane Gasperin, of the Illinois State Board of Elections.
In the southwestern Illinois city of Columbia, Gene Bergman voted for Santorum, saying Romney's version of health care reform while governor of Massachusetts is too closely connected to Obama's national plan now being challenged in the courts, Bergman said.
"In the general election, I think Romney will have a difficult time attacking Obamacare," he said, calling Obama's plan unconstitutional in terms of its individual mandate. "And that's a significant issue to me."
Don Gramer, who works for the Catholic diocese in Rockford, said Romney's history regarding health care reform has raised troubling questions.
"Does he really believe in less government or does he believe in just as much government as Obama does?" asked Gramer, after voting for Santorum.
The lagging campaigns of Texas Rep. Ron Paul and former House Speaker Newt Gingrich got votes, and polling officials said at least a few voters said they were Democrats but asked for Republican ballots.
Betsy Owens said she considered doing just that. The staunch Democrat said she walked into the precinct thinking she would vote for Rick Santorum to help create chaos in the Republican race, as some of her family members were going to do.
"But my conscience got the better of me, so I didn't do it," said Owens, who runs a candy company.
Thanks to the once-a-decade chore of drawing new boundaries for congressional and legislative districts, Illinois voters had other big decisions to make as well.
The Democratic majority at the state Capitol drew the new maps to make life difficult for Republicans. As a result, incumbent U.S. Reps. Donald Manzullo and Adam Kinzinger were battling for political survival in northwestern Illinois.
On the Democratic side, Jesse Jackson Jr., a Chicago congressman weakened by his ties to corrupt former Gov. Rod Blagojevich and his admission of an affair, was facing a challenge from former U.S. Rep. Debbie Halvorsen, of Crete, who represented some rural areas now part of Jackson's district.
In the Legislature, at least four incumbent Republicans would be out after the primary. That's because eight lawmakers wound up facing each other under the new districts drawn by Democrats. The lawmakers at risk included the top Republican in DuPage County, a candidate for governor in 2010 and a member of the GOP's state central committee.
The primary also created awkwardness for the Democrats.
State Rep. Derrick Smith of Chicago, who was recently hit with federal bribery charges, was on the ballot. His opponent was a former Republican official claiming to be a Democrat, leaving party leaders the choice of backing a possible felon or a candidate who they consider a member of the opposite party.
Also, Cook County Democrats were to decide whether to stick with a recently appointed member of the Illinois Supreme Court or nominate someone else for a 10-year term on the bench.