(10:28 UPDATE) FOX News determined Ted Cruz the winner of the Republican Caucuses with 27.8 percent and 86 percent of the precincts reporting.
Donald Trump has 24.4 percent for second place and Marco Rubio third with 22.9 percent, according to the Microsoft app iagopcaucuses.com
The Democrat race in a dead heat has Hillary Clinton with 50.1 percent to Bernie Sanders' 49.3 percent with 91 percent of the precincts reporting according to idpcaususes.com In a distant third is Martin O'Malley (0.6 percent).
Rounding out the Republican field was Ben Carson fourth (9.7 percent), Rand Paul fifth (4.5 percent), Jeb Bush (2.8 percent), John Kasich, Carly Fiorina, Mike Huckabee, Chris Christie, Rick Santorum, Other and Jim Gilmore.
At stake in Iowa was crucial early momentum in the presidential campaign, and for some candidates, the future of their White House hopes altogether.
Candidates faced an electorate deeply frustrated with Washington. While the economy has improved under President Barack Obama's watch, the recovery has eluded many Americans. New terror threats at home and abroad have also ratcheted up national security concerns.
Early-arriving voters at Republican caucuses indicated they were deeply unhappy with the way the federal government is working. Four in 10 said they were angry and half said they were dissatisfied.
Six in 10 Democratic caucus-goers wanted a candidate who would continue Obama's policies, according to the preliminary entrance polling.
In Iowa, which has for decades launched the presidential nominating contest, candidates also faced an electorate that's whiter, more rural and more evangelical than many states. But, given its prime leadoff spot in the primary season, the state gets extra attention from presidential campaigns.
Iowa has decidedly mixed results in picking eventual nominees. The past two Republican caucus winners -- former Arkansas Gov. Mike Huckabee and former Pennsylvania Sen. Rick Santorum -- faded as the race stretched on. But Barack Obama's unexpected 2008 victory was instrumental in his path to the Democratic nomination, easing the anxieties of those who worried the young black senator would struggle to win white voters.
Clinton was seeking to overcome the ghosts of her loss to Obama in 2008. Her campaign spent nearly a year building a massive get-out-the-vote operation in Iowa.
Yet she faced an unexpected challenge from Sanders, the self-declared democratic socialist from Vermont. Sanders has drawn big, youthful crowds across the state and his campaign was hoping for high turnout.
"We will struggle tonight if the voter turnout is low. That's a fact," Sanders told volunteers and supporters in Des Moines.
-- The Associated Press contributed to this report