No new polls have been released since he jumped into the race, and O'Rourke over the weekend refused to release fundraising numbers from his first day on the trail - a standard marker of early interest and enthusiasm in presidential races - which was expected to be O'Rourke's strength after he broke fundraising records during his Senate campaign previous year.
The stunning sum is more than rival Bernie Sanders and every other 2020 Democratic challenger who has disclosed their first-day fundraising totals.
At the tail end of that race, from July to September 2018, O'Rourke had raised more than $38 million, the most any candidate for the U.S. Senate had ever raised in a similar period.
"In just 24 hours, Americans across this country came together to prove that it is possible to run a true grassroots campaign for president-a campaign by all of us for all of us that answers not to the PACs, corporations, and special interests but to the people", a campaign statement quoted O'Rourke.
O'Rourke kicked off his presidential campaign on Thursday with a video on social media and a three-day visit to Iowa, which will hold the first presidential nominating contest in February 2020.
The rising star's online fundraising haul managed to beat out Senator Bernie Sanders' record of $5.9m last month in the first 24 hours of his campaign.
Sen. Elizabeth Warren, D-Mass., raised at least $300,000 on New Year's Eve, her first partial day in the race, according to filings from the online donation clearinghouse ActBlue.
Democrats have sworn off big money in their challenge to Republican President Donald Trump, who began his re-election campaign this year with $19.2 million in cash.
Most of the other Democratic candidates have not publicized their own first financial tallies, except for Sen. Kamala Harris with $1.5 million in the first 24 hours, former Colorado Gov. PACs refers to Political Action Committees.
Candidates will officially report their fundraising totals for the first quarter to the Federal Election Commission on 15 April.