The survey of more than 30,400 U.S. adults was conducted from April 1 to May 31 as part of the Gallup-Healthways Well-Being Index.
The uninsured rate decreased more among blacks than it did in other major demographic groups, falling 6.2 percentage points to 14.7 percent.
The uninsured rate among Hispanics was down 5.6 percentage points since the end of 2013 down to to 33.1 percent.
Overall, the percentage of U.S. adults lacking health insurance was 17.1 percent in the fourth quarter of 2013. It dropped to 15.6 percent in the first quarter of 2014.
Studies suggest most newly insured U.S. adults paid their first premiums for their new health insurance policies, Gallup said.
The margin of error was 1 percentage point.