"More than 4.2 million Americans have signed up for affordable plans through the marketplace," Kathleen Sebelius, secretary of the U.S. Department of Health and Human Services, said in a statement.
"Now, during this final month of open enrollment our message to the American people is this: you still have time to get covered, but you'll want to sign up today -- the deadline is March 31."
The five-month total for enrollment in private U.S. health insurance via the online health insurance marketplace reached 4.2 million in February.
The report said 4,242,300 people selected marketplace private health insurance plans from Oct. 1, 2013, through Mar. 1, including 1.6 million in the state-based marketplaces and 2.6 million in the federally-facilitated marketplace.
About 943,000 people enrolled in the Health Insurance Marketplace plans in the February reporting period, which concluded March 1.
Of the more than 4.2 million:
-- 55 percent were female and 45 percent male.
-- 31 percent were age 34 and younger.
-- 25 percent were between the ages of 18 to 34.
-- 63 percent selected a Silver plan, up 1 percentage point over the prior reporting period, while 18 percent selected a Bronze plan, down 1 percentage point.
-- 83 percent selected a plan and were eligible to receive financial assistance.
The proportion of marketplace plan selections by persons between the ages of 18 and 34 increased. Persons ages 18 to 34 were 25 percent of all marketplace plan selections for the first five months of the initial open enrollment period -- compared to 24 percent during the first three months of the initial open enrollment, and 27 percent during the months of January and February.
The report also said that by March 1, 4.4 million were determined eligible for Medicaid or the Children's Health Insurance Program.
Private health insurance sign-ups were below the original goal of 5.6 million by the end of February. The Congressional Budget Office projected 7 million would sign up for health insurance by the end of March.
Last month, the budget office downgraded those projections to 6 million total for the full six-month enrollment period.