President Obama’s 2010 overhaul of the nation’s health insurance system appears to have helped significantly reduce the number of uninsured American young adults, according to a new Gallup survey and U.S. Census data.

The percentage of 18- to 25-year-olds without health insurance dropped 3.6 points since the third quarter of 2010, when a key provision of the Affordable Care Act allowing many young adults to remain on their parents’ health plans first took effect, Gallup found.

Roughly one quarter – 24.4 percent – now report being uninsured, down from 28 percent late last year. The decline represents nearly 1 million more young adults who now have health insurance, according to official estimates based on the Gallup data.

“Going without coverage puts every young American just a car accident or surprise diagnosis away from a lifetime of medical debt or worse,” said Health and Human Services Secretary Kathleen Sebelius. “The good news is today one million young adults are no longer living with that fear and uncertainty.”

The Gallup findings were corroborated by a separate U.S. Census analysis released earlier this month that also noted a decline in uninsured young adults and simultaneous increase in those with coverage.  Both studies attributed the change to the Affordable Care Act.

Democrats and the White House have hailed the findings as evidence the controversial health care law is having a positive effect, despite popular skepticism of the law and a Republican-led campaign to repeal it.

Half of all Americans oppose the law, fearful of a perceived negative impact on the economy and federal deficit, a recent ABC News/Washington Post poll found. Fewer – just 37 percent – said they favor repealing all or part of the law.

Some provisions, including the mandate allowing young adults under age 26 to remain on their parents’ health insurance and a ban on restrictions for preexisting conditions, remain popular.

Administration officials said today that an individual insurance mandate and other measures aimed at expanding insurance options would have the biggest impact on reducing the overall number of Americans without health insurance when they take effect in 2014.   But they’re also among the most unpopular.

The mandate alone faces constitutional challenges in several ongoing cases that will likely reach the U.S. Supreme Court. Republicans have also vowed to do everything they can to hamstring implementation of that part of the law.

Nearly one in five Americans 25 to 64 years old does not have health insurance, according to Gallup, or roughly 30 million Americans.