14.1 million Americans have gained health plans since Obamacare's coverage expansion began in 2014. An additional 2.3 million young adults gained coverage between 2010 and 2013 — after Obamacare began requiring employer plans to offer dependent coverage through age 26. Federal officials say this is the largest drop in the uninsured rate since 1965, when Medicare and Medicaid began.

America's uninsured rate just fell by one-third

A new report from Health and Human Services finds that the uninsured rate has fallen from 20.3 percent prior to the health-care law down to 13.2 percent at the start of 2015. This is a 7.1 percentage-point decrease in the uninsured rate — or, to put it another way, a 35-percent decline in the number of Americans who lack insurance coverage.

"Nothing since the implementation of Medicare and Medicaid has come close to this kind of change," says Richard Frank, assistant secretary for evaluation and planning at Health and Human Services.

The decline in coverage has coincided with two big Obamacare programs. First, there was the part of the law that required employers to offer dependent coverage up through age 26. Since that program began in 2010, the uninsured rate among young adults (Americans between the ages of 19 and 26) has dropped from 34.1 percent to 26.7 percent.

Second, and much larger, was the start of the health law's insurance expansion in 2014. Federal officials estimate that since the expansion started, 14.1 million Americans have gained coverage, largely through Medicaid and the health law's marketplaces for private insurance.