Illinois is among 24 states taking part in "Super Tuesday," the February 5 contests in which voters will choose nominees from the Democratic and Republican parties for the November U.S. presidential election.
Following are some facts about the "Land of Lincoln" and its primary:
* Polls close at 7 p.m. CST, though voting by mail has been under way since January 14. Delegates are awarded on a proportional basis.
* Of the 12.9 million people in Illinois, 9.5 million live in Chicago and its suburbs.
* Democratic candidate Barack Obama represents Illinois in the U.S. Senate and calls Chicago home, and recent polls show him leading rival New York Sen. Hillary Clinton by an average of 32 percentage points. Among Republicans, polls show Arizona Sen. John McCain leading former Massachusetts Gov. Mitt Romney by an average of 14 percentage points.
* Chicago's suburbs, balanced between the Democratic-dominated city and the rural Republican regions downstate, have historically held the balance of power in statewide elections. As the suburbs have trended Democratic since the 1990s, Democrats have taken control of state government and carried the state in recent presidential races.
* The city of Cairo, located at the state's southern tip where the Mississippi and Ohio rivers converge, is closer to Atlanta than to Chicago.
* The state's nickname "Land of Lincoln" refers to Abraham Lincoln, the president who led the country through the Civil War of the 1860s. Lincoln moved to the state when he was 21 and lived there until he became the 16th U.S. president.
* Median household income is $49,328, above the national average of $44,334. The poverty rate is 11.5 percent, below the national average of 12.5 percent.
Source: National Association of Secretaries of State, Almanac of American Politics, U.S. Census Bureau
(Reporting by Andy Sullivan; Editing by Stacey Joyce)