The number of uninsured adult Americans is dropping at a record rate, according to federal data released on Tuesday by the US Centers for Disease Control and Prevention (CDC).

The number of uninsured adult Americans dropped by more than 4% in 2014, the largest decline since 1997 when the CDC began conducting its annual National Health Interview Survey. Last year, the number of uninsured adult Americans – those 18 to 64 years old – dropped to 16.3% from 20.4% in 2013. The survey of 111,682 people did not track coverage among those 65 and older as most of them are covered through Medicare.

The drop in the number of uninsured Americans has come across the economic and racial spectrum, which can be partially attributed to the expansion in Medicaid. States that expanded their Medicaid coverage had 13.3% of uninsured adults under 65 while the states that did not expand their coverage had 19.6% of uninsured adults.

Among the states that did not expand their Medicaid coverage are Texas and Oklahoma, which had two of the highest rates of uninsured adults at 25.7% and 26.6%, respectively.

Last year was the first full year that the Affordable Care Act was in effect. The 2010 law is currently being challenged in the supreme court, where justices will decide if the states that didn’t create their own healthcare exchanges and instead relied on the federal marketplace are allowed to provide tax subsidies to their residents. A ruling is expected before the end of the month.

If the US supreme court rules in favor of those suing the US Department of Health and Human Services, more than nine million people in 34 states could lose the subsidies that make their health insurance more affordable.

Here are some of the groups that saw improvement in insurance rates since the Affordable Care Act was implemented:

By poverty

In 2014, 62.1% of poor, 41.1% of near-poor and 9.9% of not poor persons under age 65 had public coverage. Just 16.6% of poor Americans had private health coverage.

While the Affordable Care Act might have benefited different income brackets differently, all groups experienced drop in uninsured rate from 2013 to 14:

• The number of uninsured poor adult Americans – 18 to 64 years old – dropped to 32.3% from 39.3%.
  
• The number of uninsured near-poor Americans dropped to 30.9% from 38.5%.
  
• The number of uninsured not-poor Americans dropped to 8.9% from 11.4%.

There was one group of people who retained a high uninsured rate: the unemployed. More than 38% of unemployed American adults were uninsured while just 14.9% of those employed were.

By race

The survey also found that Hispanic Americans and black Americans were more likely to depend on public insurance than their white and Asian counterparts. More than 40% of black Americans and 34.6% of Hispanic Americans relied on public health insurance coverage. At the same time, 73.6% of white Americans and 73.4% of Asia Americans relied on private coverage.

All race/ethnicity groups experienced drop in the uninsured:

• The number of uninsured black Americans dropped to 13.5% from 18.9%.
  
• The number of uninsured Hispanic Americans dropped to 25.2% from 30.3%.
  
• The number of uninsured Asian Americans dropped to 10.6% from 13.8%.
  
• The number of uninsured white Americans dropped to 9.8% from 12.1%.
  

Despite the drop in the number of uninsured Americans, many still reserve judgment about the 2010 healthcare law. A recent CNN/ORC poll of 1,025 adults found that 43% of them favor the law while 55% opposed to it.