The campaign of Pete Buttigieg, the mayor of South Bend, Ind., reported that it had raised $7.1 million in the quarter but spent modestly. His campaign ended the period with $6.4 million in cash on hand.

[Some candidates have also released their tax returns in recent days. See how they compare.]

The fund-raising reports provide an early measure of how the Democratic candidates are picking up support in a crowded field. Many campaigns had already announced their overall fund-raising totals for the quarter, but the reports filed before Monday night’s deadline offered details about the money that the campaigns took in and spent in the first three months of the year.

The deadline also highlighted the steep financial challenge facing some lesser-known candidates.

Gov. Jay Inslee of Washington raised about $2.3 million in the quarter, while former Gov. John Hickenlooper of Colorado raised $2 million. Only 10 percent of Mr. Hickenlooper’s total came from donors giving $200 or less. Both candidates entered the race in early March.

Julián Castro, the former housing secretary, raised about $1.1 million.

Another Democrat who is trying to gain more attention, former Representative John Delaney of Maryland, has plenty of money — but as a result of his own wealth, not an outpouring of donations. Mr. Delaney provided $11.7 million in loans to his campaign during the first three months of the year, and his campaign ended the quarter with $10.6 million in cash on hand.