With a decisive win in the Illinois presidential primary, former Massachusetts Gov. Mitt Romney sets his sights on the bayou where Louisiana holds the next Republican primary.

"We thank the people of Illinois for this extraordinary victory," Romney told supporters in the Chicago suburb of Schaumburg. "Elections are about choices. Today, hundreds of thousands of people in Illinois joined millions of people in this country in this cause."

With 99% of precincts reporting, Romney led former Pennsylvania Sen. Rick Santorum by a 47%-to-35% margin. Texas Rep. Ron Paul was running third at 9%, while former House Speaker Newt Gingrich had 8%.

With the victory, Romney was poised to win at least 41 of the 54 delegates up for grabs in the state, giving him a total of 562, according to CNN's estimate. Santorum is second with 249, Gingrich third with 137 and Paul last with 69.

A total of 1,144 delegates are needed to clinch the GOP nomination.

Louisiana will hold its primary on Saturday.