Type of election: Primary
How it works: 66 delegates are at stake, but the statewide primary is only advisory. Delegates pledge to vote for a particular candidate and are elected individually and are not bound by the statewide results. The primary is open because Illinois doesn't require voters to register by party, but a voter can only vote in one presidential primary. 54 of the delegates are allotted via congressional districts which are given delegates based on previous performance in the 2008 presidential election, with stronger Republican districts getting four delegates instead of three.
Official election results: Illinois State Board of Elections
Republican candidates: Newt Gingrich, Ron Paul, Mitt Romney and Rick Santorum (all others have dropped out or are polling at less than 1 percent)
Democratic candidates: There is no Democratic primary.
Previous performance: In 2008, Romney finished second with more than 28.5 percent of the vote. Paul finished fourth with 5 percent of the vote. Obama won the Democratic primay with 65 percent of the vote.
Television stations: Full list
Latest polling: New York Times:
Nate Silver gives Romney a 95 percent chance of winning while giving the rest to Santorum.
Bottom line: The polls here are basically meaningless due to the rules of the particular primary. Romney should win statewide, but has Santorum (or someone else) done the work to win a bigger share of the delegates? It's possible and the polling wouldn't show that.