More than 3 million young adults have gained insurance coverage under the health law, according to the latest government estimate. Obama administration officials touted the benefit Tuesday as an example of how the law is making a difference. The Supreme Court is expected to rule on its fate this month.

“3.1 million [young adults] now have valuable protections for their finances and their health, and only the law can guarantee those protections,” said Richard Kronick, a deputy assistant secretary for the Department of Health and Human Services. In recent weeks, several insurers made public commitments to maintain under-26 coverage, regardless of the Supreme Court’s health law decision.

Beginning in September 2010, the law required insurers to cover dependents under the age of 26, allowing many children to stay on their parents’ health plans if they didn’t have coverage available through an employer.

Tuesday’s report from the National Center for Health Statistics finds that the percentage of covered adults age 19 to 25 increased from 64.4 percent in September 2010 to 74.8 percent in December 2011. This 10 percentage-point jump in 15 months translates to about 3.1 million young adults gaining coverage, according to an HHS analysis.

“That kind of response in a short period of time is unprecedented,” Kronick said.

Previously, HHS estimated that 2.5 million young adults gained coverage through June 2011. And last week, the Commonwealth Fund estimated that roughly 6.6 million gained health insurance between November 2010 and November 2011.

The latter number, however, is based on a survey which asked whether young adults joined a parent’s plan. The federal survey instead asked whether they had coverage at the time, so it does not include the many young adults who were already insured and then switched to a parent’s plan.

“Gains in coverage were particularly large for young men,” the HHS report also notes. Coverage went up more than 14 points for men age 19 to 25.

According to Sara Collins, a vice president of the Commonwealth Fund, the data shows that young men have been incorrectly stereotyped as not wanting or seeking health care. “If they have affordable insurance options available, they’ll take advantage of them,” Collins added.  Young women continue to lead in insurance coverage, 77.5 versus 72.0 percent for young men.