And the uninsured rate among adults dropped from 20.3 percent in October 2013 to 13.2 percent by March 4 of this year—the time during which Obamacare marketplaces have been selling health plans, HHS said.

A total of 16.4 million previously uninsured adults nationwide obtained health coverage since the Affordable Care Act became law, according to the U.S. Department of Health and Human Services.

Obamacare has led to the biggest decrease in the numbers of Americans lacking health insurance in four decades—with minorities and young adults seeing the largest gains in coverage, the federal government said Monday.

Terry Donald, a beneficiary of the Affordable Care Act, is flanked by Sen. Chris Murphy, Democrat of Connecticut, and Sen. Al Franken, Democrat of Minnesota, during a news conference to discuss the Affordable Care Act case being heard at the Supreme Court on March 4, 2015, in Washington, D.C.

That is a 35 percent reduction in the rate of people without health coverage. As of this month, there were about 26 million American adults without health insurance, compared to about 40 million without coverage just before the Obamacare insurance marketplaces launched in the fall of 2013.



HHS credited the large decrease in the overall uninsured rate to Obamacare's creation of those government-run marketplaces that sell health insurance, the loosening of Medicaid eligibility requirements in more than half of the country and to the Affordable Care Act provision that allows young adults to stay on their parents' health plans until they turn 26. The provision related to young adults began in 2010.



"This is an historic drop in the uninsured, and nothing since the adoption of Medicare and Medicaid even comes close," said Dr. Richard Frank, HHS's assistant secretary for planning and evaluation, during a call with reporters.



HHS Secretary Sylvia Burwell said, "When it comes to the metrics of affordability, access and quality, the evidence shows that the Affordable Care Act is working, and families, businesses and taxpayers are better off as a result."



The plunge in the overall uninsured rate was matched by drops across all major races and ethnic groups, officials said. However, minorities saw the largest decreases in their uninsured rates.

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Latinos had a 12.3 percentage point reduction in their uninsured rate, and the uninsured rate for African-Americans fell by 9.2 percentage points, HHS said. Whites saw a 5.3 percentage point reduction in their uninsured rate.

In terms of sheer number, 6.6 million white adults gained coverage, 2.3 million African-American adults added coverage and another 4.3 million Latino were newly insured, according to HHS. After those gains, just 9 percent of white adults lack health coverage, and 13.2 percent of African-American adults remain uninsured.

But Latinos, by far, retained their status as the leader among the uninsured—29.5 percent of Latino adults still lack health coverage.

Among young adults between the ages of 19 to 25, the uninsured rate dropped from 34.1 percent to 26.7 percent since 2010, the year in which the ACA was signed into law.