Paul was in a distant second place in early returns, collecting almost 17 percent of the vote.
Paul was ultimately unable to overcome strong turnout from Mormon voters in Idaho. According to a 2008 Pew Survey of the state, a plurality of those eligible to vote in the state — 23 percent — self-identify as Mormon, more than evangelical Protestants or Catholics.
Paul acknowledged as much during a radio interview Tuesday, telling Laura Ingraham that Mormon voters were rallying to Romney much in the way Catholic voters supported former President Kennedy or African-American voters supported President Obama.
"If Mitt wasn't in this race, I'd have about 70 percent of the vote," Paul said of his Idaho chances.
The other candidates did not completely ignore the state: Romney and Rick Santorum both visited Idaho earlier this year and Romney's son, Josh, spend two days campaigning there in late February.
There were no polls conducted of Idaho in the days before the primary election, so predictions of how the delegates will be allocated will prove difficult until the state party reports its final results.