US Census Bureau data show 16 percent of Pima County residents under the age of 65 did not have insurance in 2014.
That is the lowest rate of uninsured residents since the Census Bureau began tracking the statistic on a county-by-county basis in 2006.
The Bureau also released statistics looking at the percentage of uninsured individuals based on income. It showed a drop for all Pima County residents making less than 400 percent the federal poverty level.
Arizona's uninsured rate is 0.1 percent higher than Pima County, but 2.5 percent higher than the national average.
2014 was the first year that the Affordable Care Act's insurance mandate was in effect.