New data from the U.S. Census Bureau present the most detailed picture yet of the dramatic rise in the number of people covered by health insurance since the Affordable Care Act went into effect.
County-level data going back to 2010, when the law was signed, show a patchwork of people living without health insurance that ticked down slowly for the first three years under the ACA. But once the online insurance exchanges opened at the end of 2013 and Medicaid expanded, the population living without coverage dropped noticeably.
The recently released census report is county-level data for 2015. Overall, the nationwide uninsured rate dropped 7.7 percentage points for people under 65 years old between 2010 and 2015, from 18.2 percent in 2010 to 10.5 percent in 2015.
Although the opening of the online exchanges and Medicaid expansion contributed most noticeably to the increase in the number of people with health insurance, other elements of the health care bill went into effect earlier.
For example, since 2010 the law has allowed young people to stay on their parents' health insurance until age 26.
A year-by-year breakdown of the county-level uninsured rate shows how the portion of the population with health insurance has risen as the Affordable Care Act has gone into effect. It also shows the persistent differences in insurance coverage by state and county.
According to the census data, the U.S. counties with the top five reductions in the number of uninsured people between 2010 and 2015 are large, urban counties: Miami-Dade County, Fla.; Los Angeles County, Calif.; Orange County, Calif.; Cook County, Ill.; and Harris County, Texas.
In 2012, the Supreme Court upheld the Affordable Care Act but gave states a choice about whether to expand Medicaid to cover more of their citizens. Under the Medicaid expansion, the federal government made money available to state governments to cover the costs of low-income people who were not previously eligible for Medicaid.
Today, 31 states and the District of Columbia have expanded Medicaid. In most of those states, the expansion took effect in 2014, when the online health insurance exchanges also went live.
As NPR's Alison Kodjak has reported, a handful of states that first rejected the expansion have since embraced it, including Louisiana and Montana.
And nationwide, a lot more poor people are covered by health insurance than were before the Affordable Care Act.
People who do not make much money, and who are less likely to have health insurance, have especially benefited. While the national uninsured rate has dropped by 6.3 points since 2013, it has dropped by 8.9 points for those below the federal poverty level and by 12 points for those whose income is between 100 and 200 percent of the federal poverty level.