The percentage of young adults without health insurance decreased by about four percentage points since the implementation of a provision in the federal health reform law allowing them to remain on their parents’ coverage, according to a Gallup poll.

The survey follows a U.S. Census Bureau report released last week that found that 72.8% of people ages 18 to 24 had health coverage in 2010, up from 70.7% in 2009.

The Gallup poll — which surveyed 89,857 individuals between April 1 and June 30 — found that the rate of U.S. residents ages 18 to 25 without insurance declined from 28% in fall 2010 to 24.2% in the second quarter of 2011. That translates to about one million more young adults with health coverage.

According to Gallup officials, the increase began in January, after most employer-sponsored health plans were required by a provision in the overhaul to allow adult children to remain on their parents’ plans until they turn 26.

The survey did not indicate a drop in the number of uninsured U.S. residents in other age groups.