Another front-runner, Sen. Barack Obama, D-Ill., and other GOP candidates had yet to release their totals.
Romney collected an estimated $23 million during the first quarter of this year, his campaign reported, placing him ahead of the other two Republican front-runners Sen. John McCain, R-Ariz., who received $12.5 million, and former New York Mayor Rudolph Giuliani, who brought in $15 million.
"Governor Romney's fundraising totals are indicative of the extraordinary success the campaign has had at building an organization and stirring excitement among grassroots activists responding to his message," Romney spokesman Kevin Madden told the Associated Press.
On the other side of the aisle, Clinton's campaign reported Sunday that it had received $26 million in new contributions, shattering the record by any candidate, Democratic or Republican, for the same period set at $8.9 million by Al Gore in the first quarter of 1999.
"We dramatically exceeded our goals and expectations," Patti Solis Doyle, Clinton's campaign manager, told the Washington Post.
Clinton raised $10 million over the last two weeks in March, including $600,000 in the final 36 hours, according to the Washington Post.
Clinton's total eclipsed the $14 million raised by former North Carolina Democratic Sen. John Edwards, which included $3.3 million in online donations, but Edwards' campaign remained undaunted.
"History has clearly indicated that the most money is not the key to the nomination," said Jonathan Prince, Edwards' deputy campaign manager, in a statement.
Though Obama has not yet announced his fundraising totals, aides said he had more than 83,000 donors when reports were filed to the Federal Election Committee on March 31.
"I think that we will have raised enough money to make sure we can compete for the next quarter and beyond. I think we'll do pretty well," Obama said in an interview Sunday with the Associated Press.
Other Democrats who released fundraising numbers included New Mexico Gov. Bill Richardson with $6 million, Sen. Chris Dodd, D-Conn., who reported raising $4 million, and Sen. Joseph Biden, D-Del., who had $3 million.