Mitt Romney has polled well ahead of Rick Santorum in Illinois the last few days, but his campaign told the Huffington Post that they expect the race to be closer than the polls predict. Santorum doesn't appear to agree, though: he's flying to Pennsylvania tonight. His speech after polls close will be delivered from Gettysburg, which the Associated Press says is Santorum's symbolic nod to Illinois' Abraham Lincoln. However, the town is also the site of the worst mass slaughter of the Civil War, in which Robert E. Lee's invasion of the North was crushed. That's less pleasant symbolism for an insurgent candidate. 

The primary by the numbers:
Delegates: 69. Only five states award more. But only 54 will be selected today.
Unbound delegates: 12, selected in June at the state party's convention.
Delegates Santorum can't win: 10, because he didn't fill out delegate slates in all the congressional districts. He had a similar problem in Ohio.
Money out: Romney outspent Santorum 7 to 1.
Money in: In February, Romney raised $11.5 million, Santorum raised $9 million, Paul raised $3.3 million, Gingrich raised $2.6 million -- and has $1.5 million in debt.
Polls: Romney is averaging a 10-point lead over Santorum, according to Real Clear Politics. But Santorum has consistently performed better than polls predict.
 
We'll be liveblogging the returns starting at about 7p.m. Eastern time, an hour before polls close. Be sure to join us in the comments!
 
Updates: 
 
10:01p.m.: Romney did what he has so far had not been able to do tonight. No, not win evangelicals -- he still lost those guys. But his campaign managed to not make a victory look lame by declaring he'd win big in advance. With 61 percent reporting, Romney has 48 percent and Santorum has 35 percent. (Paul is beating Gingrich for third.) Romney finally looked a little relaxed -- he even let through some real smiles -- during his victory speech. He was surrounded by women, but exit polls showed that unlike in earlier states, he actually performed better among men. Santorum was his angry self, though he did steal a line from Newt Gingrich: that this is the most important election since 1860. (Not everyone shares this analysis.) Santorum has turned to campaigning in Pennsylvania, while Romney has turned, for what feels like the millionth time, to going after Obama. We'll see if it sticks. Louisiana votes March 24, and Santorum is polling 13 points ahead.
 
9:58p.m.: Santorum vows to fight till his homestate, where he says he'll win lots of delegates. While he revived his campaign by winning in the Midwest, he's lost several big states there recently: Michigan, Ohio, and now Illinois. 
 
9:53p.m.: "Low turnout tonight. A nominee that depresses turnout won't beat @BarackObama. Still time for a conservative," Newt Gingrich tweets. As polls come in, he's slipping below Ron Paul. With 56 percent of precincts reporting, Paul has 9 percent and Gingrich has 8 percent.
 
9:48p.m.: If Santorum were a little older, he'd be the mean old man in the neighborhood who won't give you your baseball back when you it into his yard. In the bottom right corner, that's his face after he tells a joke that gets huge cheers.
 
9:42p.m.: Santorum's scrappy campaign is known for its bad lighting at campaign appearances. It looks really bad tonight on C-SPAN:
 
And better, but not much, on CNN:
 
9:37p.m.: "Romney unable to break through with key constituencies tonight, like voters who do not like Mitt Romney," The New York Times' Nate Silver tweets.
 
9:35p.m.: With 47 percent of precincts reporting, Romney has 50 percent and Santorum has 33 percent.
 
9:32p.m.: But Romney still looks uncomfortable sometimes during his applause lines. Here, he said he would make the military so strong no one would try to test it. How big would that have to be? The U.S. military is already better financed that most of the world's militaries combined.
 
 
9:30p.m.: Romney's giving a better speech than usual -- he even got the crowd to laugh twice. He's ignored Santorum and only criticized Obama, using some classic conservative lines like mocking Obama's past as a law professor.
 
9:22p.m.: Romney always looks more genuine on nights he wins. 
 
9:16p.m.: A marital moment as Ann introduces her husband.
 
 
9:07p.m.: With 31 percent of precincts reporting, Romney has 54 percent to Santorum's 29 percent.
 
9:01p.m.: Santorum's new theme is "Freedom." That is reportedly why he's going to riff on Abraham Lincoln from Gettysburg tonight. This will include freedom from government intervention into healthcare. But any Ron Paul fan will tell you Lincoln has a mixed record on freedom -- he freed the slaves but was a gross violator of habeas corpus.
 
8:50p.m: Romney's victory party crowd is filling up, and he's expected to speak in about 10 minutes.
8:47p.m.: With 20 percent of precincts reporting, Romney has 56 percent to Santorum's 27 percent.
 
8:43p.m.: NBC and CNN join Fox in projecting Romney as the winner. Fox has been first in most of these primary races, going back to Iowa, when Karl Rove had the inside scoop on what was in the missing vote tallies.
 
8:41p.m.: With 8 percent of precincts reporting, Romney has 54 percent, Santorum 28 percent, Paul has 10 percent, and Gingrich has 7 percent. The New York Times' map indicates most of the ballots counted have come from cities and suburbs, which is where Romney does well.
 
8:34p.m.: Fox News declares Romney the winner.
 
8:33p.m.: With 1 percent of precincts reporting, ROmney has 54 percent, Santorum has 29 percent, Paul has 10 percent, and Gingrich has 6 percent.
 
8:32p.m.: NBC News' Chuck Todd points out that Romney loses among the very conservative only because so many of them are evangelicals. He and Santorum are tied among very conservative non-evangelicals.
 
8:28p.m.: Protesters outside Santorum's rally in Gettysburg:
(Photo via Reuters.)
 
8:24p.m.: Romney won more than half of non-evangelicals -- 52 percent. Santorum won evangelicals.
 
8:13p.m.: One of these campaigns is better at setting up election parties than the other:
Santorum's above, Romney's below.
 
8:10p.m.: The only age group Santorum won was people in their 40s.
 
8:07p.m.: One of the odd things that's happened since contraception became part of the GOP primary is that while independent women have soured on on Republicans, Republican women have started liking Santorum -- the family values guy -- more and more. Tonight CNN exit polls show Romney has a tiny gender gap, even though for the first few primaries, he performed better among women. This time, he won 46 percent of men and 44 percent of women. Santorum won 32 percent of men but 38 percent of women.
 
8:02p.m.: Polls have closed. Romney is leading, but no networks have called.
 
7:55p.m.: Record low turnout tonight, the Chicago Tribune reports. At 2p.m. it was 15 percent; the current record holder is 1996, when turnout was 32 percent.
 
7:36p.m.: Santorum has been urged to smile a lot during this primary. It doesn't appear to come naturally. Here he is defending his line that he doesn't care about the unemployment rate:
Not smiley. But he looked like he was trying his hardest to smile Monday on MSNBC's Morning Joe. He made his usual angry face while answering each question, but when he quit talking, he'd smile awkwardly every time:

 
7:34p.m.: Romney outspent Santorum 7 to 1 in Illinois, but almost 60 percent of voters in the state say the ads played little to no role in their vote, The New York Times points out. Santorum's superPAC spent $530,111 on ads, while Romney's superPAC spent $4 million. All for nothing, if voters are telling the truth. Does anyone ever look at those numbers and calculate how many times that sum could have paid off your student loans? No? Just me? (The answer is: so many times.)
 
7:24p.m.: Romney's Secret Service protection while he speaks in Peoria, Illinois. His code name is reportedly "Javelin." 
(Photo via Associated Press.)
 
7:19p.m.: Exit polls show Republican voters aren't tired of the primary at all. A third say they want the contest to keep going even if their guy loses; two-thirds they want it to go on for months as long as their guy wins. Well, we've got a little bit of bad news for them: ABC News' Michael Falcone reports that Santorum's campaign expects it to be an early night. As in the margin will be wide enough to declare the winner quickly.
 
7:10p.m.: It looks like Republican voters are splitting in familiar ways: exit polls show Romney winning urban areas, moderates, the well-educated and well-off, while Santorum winning the boonies, conservatives, and the less educated and less wealthy. More than 40 percent had "reservations" about their candidate, the Wall Street Journal reports.