Campaign spokeswoman Meredith Kelly said Sunday that nearly two-thirds of Gillibrand's donors are women, 92 percent were under $200 and the average online donation was $25.
Kelly added that the New York Democrat's campaign has $10.2 million cash on hand.
Gillibrand's fundraising trails all five of her Senate colleagues who are seeking the Democratic nomination. Vermont Sen. Bernie Sanders has raised more than $18 million; California Sen. Kamala Harris was at $12 million. Massachusetts Sen. Elizabeth Warren has raised $6 million, Minnesota Sen. Amy Klobuchar has raised $5.2 million and New Jersey Sen. Corey Booker has raised $5 million. The senator from New York also lags behind former Texas congressman Beto O'Rourke, who hauled in $9.4 million in the first 18 days of his campaign and South Bend, Ind., Mayor Pete Buttigieg, who raised $7 million in the first quarter — and finally declared his candidacy Sunday.
Gillibrand is ahead of New York-based entrepreneur Andrew Yang, who reported raising $1.7 million in the first quarter. The remaining candidates have until Monday to file their fundraising reports with the Federal Election Commission.
Campaign cash, along with polling, is a much-watched barometer of a candidate’s clout, strength, and popularity.
Aides to Gillibrand's campaign have viewed her candidacy in two distinct phases. The first "exploratory" phase began in January when Gillibrand revealed that she was considering a presidential run on during an appearance on "The Late Show with Stephen Colbert. She then quickly made her first trip to the leadoff caucus state of Iowa and held 60 events across eight states.
The second phase began with the formal launch of her campaign on March 17. Since then, her campaign said she doubled her total number of donors, though the campaign did not disclose the total number of donors or donations to her campaign.
In a memo to supporters obtained by The Associated Press, Gillibrand's campaign also says that she received a fundraising boost from her recent appearance at a CNN town hall. In that memo, Gillibrand's campaign says that of donations to the campaign made within 48 hours of the April 9 town hall, 63 percent were new contributors.
In the same memo, her campaign said though it saw her on strong financial footing, her decision to call on former Sen. Al Franken, D-Minn., to step down over allegations of sexual misconduct had an adverse impact.
In the memo, the campaign said there was "no question that the first quarter was adversely impacted by certain establishment donors – and many online – who continue to punish Kirsten for standing up for her values and for women."
Fox News' Paul Steinhauser and The Associated Press contributed to this report.