WASHINGTON -- Twenty million previously uninsured people have gained health coverage since the Affordable Care Act became law in 2010, President Barack Obama said during a speech in Milwaukee Thursday.

Obama's announcement was based on a report the Department of Health and Human Services published the same day, which found 17.7 million working-age adults became insured between the beginning of Obamacare's first enrollment period in 2013 and the close of this year's sign-up campaign last month. The department estimates 2.3 million adults under the age of 26 got covered through the law's provision allowing young adults to remain on their parents' policies.

These findings, based on several surveys, are merely the latest proof that, whatever its shortcomings, the Affordable Care Act has succeeded in its primary goal of reducing the number of Americans who lack health insurance. The share of adults aged 18-64 without health insurance was 11.5 percent as of February, down from 20.3 percent in October 2013, according to the report. Other polls that include children and people over 65 show an even lower uninsured rate .

"This is the lowest rate that we have seen since we started keeping these records," Obama said. "We're not going backwards. We're not going to go back to a time where people could be denied because of pre-existing conditions. That's not who we are. That's who we were."

Obama traveled to Milwaukee because the city bested other locations in a challenge to sign up the most people in the enrollment period that recently ended. Close to 13 million enrolled in private coverage via the Obamacare health insurance exchanges this year.