Ted Cruz, who has defeated the businessman in seven states.
The man held the Trump sign up as a police officer led him out of the Peoria Civic Center.
On the Republican side, Texas Sen. Cruz asked voters in Rockford, Illinois on Monday.
Protesters are not as common at Cruz campaign stops as they are for Donald Trump, where fear of violence led to cancelation of a Trump event on Friday night in Chicago.
Clinton's pitch came as Trump blamed Sanders supporters for protests that prompted the billionaire mogul to cancel a rally at the University of IL at Chicago - just a few miles away from the union hall where Clinton wooed supporters.
Clinton leads Bernie Sanders just 46/41 in OH and 48/45 in IL, while narrowly trailing Sanders in Missouri 47/46. "We know that from the last two democratic presidents. Secretary Clinton should explain to the people of MI how they have benefited from the outsourcing of their manufacturing jobs", Weaver said.
US Democratic presidential candidate Hillary Clinton looks on during a Get Out the Vote event at Grady Cole Center on March 14, 2016 in Charlotte, North Carolina.
Cruz says the media has lost focus on issues that matter to voters. Clinton said immigrants have to go through a process where they are vetted and screened.
Democrats, meanwhile, are already digging in for a long struggle, though the electoral mathematics of the race suggest Sanders must start to pull off large victory margins if he is to overtake Clinton's lead of around 200 pledged delegates. Instead, his campaign push could actually give both states and all 165 delegates to Trump, which would actually make him a virtual lock for the endorsement.
Cook County Clerk David Orr says it won't be immediately clear how many voters cross over from one party to vote in another party primary.
He's betting his criticism of trade deals will hurt Clinton in Illinois, Missouri and Ohio. Why Hillary Clinton's win in the Northern Marianas matters. However, this year, the presidential primaries for both Democrats and Republicans are still up in the air.
Here's the state of play and what to watch in each state, ordered by poll closing time.
"If he's not the nominee, then I think Hillary will benefit as did Barack Obama when she challenged him all the way to the end", Devine said.
Florida and OH are the big prizes sought by front-runners Donald Trump and Hillary Clinton, as they aim to prevent rivals from narrowing the delegate gap. But Illinois and Missouri? There is a blame candidate and a responsibility candidate in this race.
Trump was not the only politician Clinton knocked on Monday. Watch to see if he spends more time trying to nudge Rubio and Kasich out of the picture, or takes it to straight to Trump.
Hillary Clinton had hoped Tuesday's primaries in five states in the South and Midwest would cement her grip on the Democratic presidential nomination. Sanders returned to Chicago for a late-night rally on Monday, which drew almost 4,000 people to the historic Auditorium Theater. He will begin the day in Rockford at the Coronado Performing Arts Center.