Obama's campaign said via Twitter on Saturday that 1,825,813 people donated to the campaign last month. Of that, 567,000 were new donors.
A vast majority of the donations 98 percent were $250 or less.
The average contribution was $53. "That's by far our biggest month yet," campaign manager Jim Messina said in an email to supporters, urging them to chip in even more as the Nov. 6 election draws near.
Republican presidential candidate Mitt Romney's campaign has not yet released its September fundraising figures, which are also expected to be high. A spokeswoman declined to say when the results would be made public.
Obama's campaign and the Democratic National Committee raised more than $114 million in August, just beating Romney's $111 million. That followed three months when Romney out-raised the incumbent.
The big September number is another piece of good news for Obama after a jobs report on Friday showed unemployment had dipped to 7.8 percent.
The campaign hoped its fundraising success and the jobs report would shift attention from the president's lackluster debate performance on Wednesday against Romney, whose aggressive showing gave his own campaign a boost.
A Romney spokeswoman said his team had raised $12 million online after the debate in less than 48 hours, with 60 percent of the money from first-time donors.
Obama's September haul was his biggest of this election cycle, but slightly lower than four years ago, when his campaign and the DNC together brought in $193 million in September.
Obama advisers are proud of his campaign's base of low-dollar donors, believing that gives the president an advantage, especially at the end of the election cycle when supporters can keep giving even if they have donated before.
Since the campaign officially kicked off in April 2011, 3.9 million people have donated, it said.
Obama's muted debate performance may increase the need for infusions of cash to fund ads in swing states such as Ohio, Florida and Iowa.
Both candidates continue to raise money even in the final month of the campaign, reflecting the importance of deep coffers to fund the last flurry of expensive advertising.
Obama leaves on Sunday for a fundraising trip to California in an effort to make October a strong month as well.
"We need every last dollar to continue to build the largest grassroots campaign in history, communicate with the American people and compete against the special interest money flooding in from the Republican Super PACs," campaign spokeswoman Jen Psaki said.
Republicans have had greater success in raising funds from outside groups known as Super PACs or political action committees, which can spend unlimited amounts on advertising.
Former President Bill Clinton will join Obama at a fundraiser in Los Angeles at a private residence with 12 attendees, the campaign said.
Obama then speaks at an event with some 6,000 people that will feature music from singers Jon Bon Jovi and Jennifer Hudson as well as remarks from actor George Clooney.