Three groups that long had the toughest time affording health insurance were the biggest beneficiaries of Obamacare's goal of reducing the number of people without coverage, a new survey shows.
The Commonwealth Fund survey found that those groups—young adults, Latinos and the poor—saw larger drops in their uninsured rates after the launch of Obamacare than any other group.
The uninsured rate for people age 19 to 34 years old fell from 28 percent last summer to 18 percent as of June—meaning there were 5.7 million fewer uninsured young adults. That age group's 10-percent drop contrasts with the 3-percent drop seen by each of the two older age groups broken out by the survey.
The uninsured rate among Latinos fell from 36 percent to 23 percent, a much bigger drop than the four-point decrease seen among whites and the 1-point drop among blacks, according to the Commonwealth Fund.
And the uninsured rate of people earning less than 2.5 times the federal poverty level fell by about 10 percent, significantly outpacing groups who earn more money, according to the private foundation, which specializes in health-care research.
But the number of poor people who lacked insurance was essentially unchanged in the 25 states that had had not expanded eligibility for government-run Medicaid coverage by April, according to the survey.
And those non-expansion states ended up with much higher percentages of uninsured poor people than in the non-expansion states.
Nationally, the rate of working-age adults without health coverage dropped from 20 percent last year to 15 percent as of June, the report found.
"Twenty million Americans have gained new coverage under law," said Commonwealth Fund President Dr. David Blumenthal.
And the survey also found that the majority of those who were newly covered either by Obamacare insurance plans or Medicaid said both that they are optimistic about that coverage getting care they need, and that they had already used it to visit a medical provider or fill a prescription.
Sixty percent of the newly covered had gone to a doctor or hospital or filled their prescription as of June, and 62 percent said they wouldn't have been able to pay for or access such care before getting that new coverage.
Slightly more than half of the respondents said their new insurance plan included all or some of the doctors they desired. Fifty-eight percent of the newly covered said they were better off than before they got that coverage.
Commonwealth Fund Vice President Sara Collins, lead researcher on the survey that questioned more than 4,425 people between the ages of 19 and 64, said the report is the first to examine both trends in coverage due to Obamacare and how people have used their new insurance.
"The findings suggest that the Affordable Care Act is beginning to achieve its central goal—reducing the number of Americans who are uninsured, and improving access to health care," Collins said. "Adults who are being helped the most are those who historically have had the greatest difficulty affording health insurance and getting the care they need."
The ACA, which mandates that most Americans have some form of health coverage or pay a penalty, has two primary tools to help millions of uninsured people afford such coverage.
This first is the federal subsidy, or tax credit, available to many low- and middle-income people to help them buy insurance plans sold on government-run Obamacare exchanges, which opened for business last fall.
The second is the expansion of Medicaid eligibility requirements to allow most poor people to be covered by that program. While the ACA originally mandated that all states expand Medicaid, which they jointly run with the federal government, a 2012 Supreme Court decision left it up to individual states to decide whether to expand or not.
The report found that 63 percent of people who since last summer had obtained health coverage through the new Obamacare exchanges or via Medicaid were previously uninsured.
The expansion of Medicaid benefits as well the phenomenon of previously eligible people enrolling in new coverage for the first time, significantly lowered the uninsured rate among the poor, the survey found.
As of last summer, 33 percent of people who earn less than 100 percent of the federal poverty level, or $11,670 annually for an individual, were uninsured. That had fallen to 26 percent as of June, according to the survey.
But most, if not all of that decrease came in the 25 states and the District of Columbia that had expanded Medicaid eligibility by April.
In those states and D.C., the uninsured rate among those poor people fell from 28 percent to 17 percent.
In the so-called non-expansion states, which started from a much higher uninsured rate of 38 percent for those poor people last summer, the rate fell to 36 percent. But that was a statistically insignificant decrease, the survey's authors said.
The effect of states not expanding was dramatically illustrated by the case of Texas, whose governor is hostile to Obamacare altogether.
The Long Star State, which at 34 percent had the highest uninsured rate in the nation as of last summer, saw a very big drop in that rate, down to 22 percent. But Texas, and Florida, another non-expansion state, still have the highest uninsured rates of any large state.
In contrast, California, which expanded Medicaid and enthusiastically embraced Obamacare, saw its uninsured rate among working-age adults plummet from 22 percent to 11 percent.
The Commonwealth Fund survey came on the heels of a report by WalletHub that looked at uninsured rates of individual states.
The WalletHub report found that the states with the lowest uninsured rated were overwhelmingly "blue states"—ones lead by Democrats who embraced Obamacare through running their own insurance exchange and expanding Medicaid. The highest uninsured rates tended to be seen in "red states," lead by Republicans and hostile to Obamacare.
WalletHub noted that "nearly 1 in 4 Texans lack health insurance . . . compared to just 1 in 100 residents in Massachusetts," which had the lowest rate of uninsured people in the nation.
—By CNBC's Dan Mangan