Former Massachusetts governor Mitt Romney swept to victory in the Republican primary in Illinois on Tuesday, winning by a wide margin, US television networks projected.
Fox News and CNN both showed Romney winning the race with 56 per cent of the vote, to 27 per cent for former Pennsylvania senator Rick Santorum, his nearest rival.
The victory took Romney another step closer to clinching his party's nomination to run against President Barack Obama in November.
The projections showed Texas congressman Ron Paul and former House speaker Newt Gingrich trailing well behind the frontrunners, with nine and seven percent of the vote respectively.