Trump, with just one day's notice on a weeknight, was able to fill to capacity a hall that holds 700.
"I didn’t want to be here, to be honest, I wanted to be about five minutes away," Trump told the crowd. "When you’re treated badly, you have to stick up for your rights -- whether we like it or not."
Trump had said he was skipping the debate because he would not be treated fairly by Fox News anchor and debate moderator Megyn Kelly.
Speaking 15 minutes after the debate had begun, Trump said that Fox News had "called a few minutes ago" to reconsider participating
Fox News said that its chairman, Roger Ailes, had three conversations with Trump and said in a statement that Trump had offered to participate in the debate if Fox News donated $5 million to his charity.
Fox News declined to make the payment, calling it a "quid pro quo" in its statement.
Trump has made such a demand previously, telling CNN when it hosted a Republican debate that it should donate $5 million to charity from the profits gained from advertising.
Trump was able to garner a tremendous amount of attention on Thursday without having to share much of the spotlight. Cable news networks CNN and MSNBC provided extensive coverage of his event.
In deciding to hold a competing event, Trump said the gathering would be to benefit veterans and he welcomed his rivals to attend. Former Arkansas Governor Mike Huckabee and former U.S. Senator Rick Santorum of Pennsylvania joined Trump after participating in the undercard debate held for the Republican candidates at the bottom of the polls.
Trump told the crowd that in one day he raised more than $5 million for a veterans group, although his campaign did not say which group was getting the funds.
Trump said he personally donated $1 million.
Trump's decision to skip the debate was sharply criticized by his opponents.
THE COMMITTED AND THE CURIOUS
There are risks in holding his own event for Trump, who several recent polls have shown barely leading U.S. Senator Ted Cruz.
If Trump wins the Iowa caucuses, the move will be lauded as proof that he has built a movement capable of circumventing establishment media. If he places second, the skipped debate will be blamed as a fatal tactical error that allowed opponents to paint him as weak in the fact of tough questions.
Trump acknowledged that he did not know whether the event would ultimately hurt or help his campaign.
"Who the hell knows, but it’s for our vets," he said.
Supporters and some curious onlookers waited in the sub-freezing cold in a line that wrapped around the building and down a block.
Trump's campaign erected a large Jumbotron outside the auditorium to allow an overflow crowd to watch his remarks.
Before Trump took the stage, some of his well-known supporters spoke. Lynnette “Diamond” Hardaway and Rochelle “Silk” Richardson, two women with a large online video blog following, urged the crowd to back Trump.
Randy Bowling, a Trump supporter from Ottumwa, Iowa, said some of his friends who are undecided in the Republican contest said Trump's decision to not participate in the debate raised doubts about supporting him.
"We have mixed emotions," Bowling said. "We caught a lot of flak from our friends who are on the fence."
Steven Doran, 19, was one of the many students and other curious area residents who attended the event with no plans to ultimately support Trump. Doran plans to participate in the Democratic caucus.
"The spectacle," Doran said when asked why he was there. "I've never seen Trump in person."
(Reporting by Ginger Gibson; Editing by Leslie Adler)
Watch the event, as posted online, below.
