CHICAGO - Pop quiz: Which state in the Republican presidential primary has the most delegates on offer: Florida, Ohio or Illinois?

If you said the latter, you're right. Illinois has 69 delegates, compared with 66 for Ohio and 50 for Florida, but it gets far less attention in the political realm than the other two key general election battlegrounds. Expect to hear a lot more about it in the coming weeks. On March 20, Illinois holds its primary, making it far and away the biggest primary prize in the month following Super Tuesday. Only Missouri - with 52 delegates - and Alabama and Louisiana - with 50 and 46 respectively - even approach the mathematical importance of Illinois.

 For GOP front-runner  Mitt Romney and rival Rick Santorum, Illinois could turn out to be  crucial. The coming 10 days shape up well for Santorum, with states like Alabama, Mississippi, Kansas and Missouri all voting. The former Pennsylvania senator could win all four.

 That makes Illinois all the more important. Victory for Romney here could prove to be a much-needed firewall to stop any Santorum momentum and reassert his position as the overwhelming favorite to win the nomination. A surprise triumph for Santorum, however, could give him an even more impressive winning streak and cause some real concern in Boston about Romney's chances of ending the primary battle anytime soon - or even winning it at all.

 At the moment, it seems, Romney is the favorite here, bolstered by the establishment - such as the backing of Illinois Sen. Mark Kirk and the state's Republican Party chairman Pat Brady - and the wealthy Chicago area. Romney is expected to spend primary night in the state, according to Greg Hinz of Crain's Chicago Business, that he is confident of a successful outing. In addition, Hinz wrote, Restore Our Future - Romney's Super Pac - has inquired about making an ad buy in the Chicago market.

 Santorum may fare better in more rural parts of the state. Nate Silver, who writes for the New York Times, tweeted last week, "Illinois is a perfect battle between the Romney coalition in the Chicago suburbs and the Santorum coalition downstate."

 But because of paperwork issues Santorum will have to overcome a disadvantage in winning delegates here. The former Pennsylvania senator did not file a full slate of delegates, so he will not be able to pick up any in four of the state's 18 congressional districts. That type of snafu already hurt his cause in Ohio, and it could again this month in Illinois.

 Even if Romney goes on to win the state on March 20, taking down favorite son President Obama in November will be another matter. Obama has enjoyed healthy double-digit leads in polls here and his campaign  expects to carry the state come this fall. In the coming months Obama is planning to return to Chicago - as well as New York City and Los Angeles - for campaign fundraisers where he will be joined by former President  Clinton.

That is a fight to be waged down the road, though. For now, Romney and Santorum have their eyes on Illinois' primary prize, the biggest one since Super Tuesday.

  Matthew Jaffe is covering the 2012 campaign for ABC News and Univision.