Like other large states, Illinois decided to move its primary forward this year, in order to increase its influence on the nominating process.

PRIMARY INFORMATION Date of primary: 5 February [Super Tuesday] Election polltracker Full state profile Q&A: US primary elections

For the Democrats, Illinois Senator Barack Obama will be expected to win his home state, although experts will be scrutinising the size of his majority to judge whether he has done as well as he should on home territory.

The Republican race in Illinois is much more competitive, with polls suggesting that John McCain is leading the pack, although that could change if Mitt Romney scores a convincing victory in Florida.

Apart from Barack Obama, the Democratic candidates have spent little time or money in Illinois. On the Republican side, campaign events are likely to increase in frequency as the day of the primary draws near.

Illinois is an industrial state, dominated by the city of Chicago, and voters here will be keen to support candidates with policies to bolster the manufacturing sector.