John Kasich has won his home state of Ohio with 45 percent of the vote, while Hillary Clinton won the state's Democratic Primary with 64 percent of the vote, according to FOX News.
The Ohio governor edged out Donald Trump (34 percent). Earlier on Tuesday Hillary Clinton and Trump won the Florida primaries.
FOX News announced that Trump had 45 percent of the GOP vote in Florida while Clinton handily won the Democratic primary with 64.7 percent.
Trump also won the Illinois GOP Primary with 40 percent of the vote, beating runner-up Sen. Ted Cruz.
Florida Sen. Marco Rubio announced he was officially suspending his campaign in a press conference.
"It was obviously not in God's plan," he said, while rebuking Trump. "Do not give into fear, do not give into frustration."
WATCH: FOXNews.com has a special digital special on Tuesday's results.
Clinton was also the projected winner of North Carolina with 58.5 percent of the vote.
For a candidate delegate tracker CLICK HERE. For an active vote tracker by FOX News, CLICK HERE.
The GOP primary is now down to three candidates: Trump, Kasich and Texas Sen. Ted Cruz. It is far from clear if any can reach the 1,237 delegates needed to clinch the GOP nomination, ratcheting up the prospects of a contested convention.
"It's a real election for someone who knows how to fix the country, the economy," Kasich said in an interview with CNN moments after the Ohio race was called. "We're fired up."
Clinton declared to cheering supporters at her victory rally: "We are moving closer to securing the Democratic Party nomination and winning this election in November."
Rubio implicitly rebuked Trump throughout a speech announcing he was dropping out of the race, imploring Americans to "not give in to the fear, do not give in to the frustration."
Rubio, a favorite of Republican leaders, is the latest candidate to fall victim to an unpredictable election cycle and Trump's unmatched ability to tap into the public's anger with Washington and frustration with sweeping economic changes.
Clinton's victories in Ohio and Florida bolstered her argument that she's the best Democratic candidate to take on Republicans in the general election. Her win in Ohio was a particular relief for her campaign, which grew anxious after rival Bernie Sanders pulled off a surprising win last week in Michigan, another important Midwestern state.
Clinton kept up her large margins with black voters, a crucial group for Democrats in the general election. Democratic voters were more likely to describe Sanders as honest, but more likely to describe Clinton's policies as realistic, according to exit polls.
Campaigning Tuesday in North Carolina, Clinton said "the numbers are adding up in my favor." She signaled an eagerness to move on to a possible general election showdown with Trump, saying he's laid out a "really dangerous path" for the country.
Votes were also being counted Tuesday in Missouri and Illinois, though races in both parties were too close to call. Trump and Cruz were in a close race in North Carolina.
Trump entered Tuesday's primaries embroiled in one of the biggest controversies of his contentious campaign. The GOP front-runner has encouraged supporters to confront protesters at his events and is now facing accusations of encouraging violence after skirmishes at a rally last week in Chicago.
The atmosphere at his events has deepened the concern over his candidacy in some Republican circles. Rubio and Kasich have suggested they might not be able to support Trump if he's the nominee, an extraordinary stance for intraparty rivals.
Trump's closest competition so far has come from Cruz, who has kept relatively close to the businessman in the delegate count. Cruz has been urging Rubio and Kasich to step aside and let him get into a one-on-one race.
Even before Tuesday's results, a group of conservatives was planning a meeting to discuss options for stopping Trump, including at a contested convention or by rallying around a third-party candidate. While such no candidate has been identified, the participants in Tuesday's meeting planned to discuss ballot access issues, including using an existing third party as a vehicle or securing signatures for an independent bid.
A person familiar with the planning confirmed the meeting on the condition of anonymity because they were not authorized to discuss the gathering by name.
Despite concerns from party leaders, Republican voters continue to back Trump's most controversial proposals, with two-thirds of those who participated in GOP primaries Tuesday saying they support temporarily banning Muslims from the United States.
The exit polls were conducted by Edison Research for The Associated Press and television networks.
Trump's Florida victory brought his delegate total to 568. Cruz has 370 delegates, Rubio has 163 and Kasich has 63. It takes 1,237 to win the GOP nomination.
Clinton has at least 1,353 delegates, including the superdelegates who are elected officials and party leaders free to support the candidate of their choice. Sanders has at least 625. It takes 2,383 to win the Democratic nomination.
--The Associated Press contributed to this report.