More than half a million Washington-area residents under 65 years of age don't have health insurance, and nearly one of every three of them is living at or near poverty, new census data released Wednesday show.

D.C. boasts the region's most comprehensive coverage for its low-income residents, with just 13 percent uninsured, while Northern Virginia has the region's worst rates, with up to 44 percent of low-income residents uninsured in Loudoun County. Suburban Maryland's rate is slightly better, with roughly one-third of low-income residents uninsured.

The region's 550,667 uninsured residents under age 65 make up about 13 percent of the area's total residents under 65.

Uninsured and under 65
In Virginia, Maryland and the District, there are 550,667 residents without health insurance.
  All under 65 Low-income*
Loudoun 8.7% 44%
D.C. 9% 13.1%
Arlington 12% 40.7%
Fairfax 12.9% 47.9%
Montgomery 13.2% 34.7%
Alexandria 15% 41.2%
Prince William 15.5% 40.6%
Prince George's 17% 31.7%
*Earning at or below $31,809 for a family of four

The varying coverage depends on different philosophies about who should be eligible for government-subsidized health care. Rates could change dramatically if health care reform that requires coverage of all Americans takes effect in 2014.

The District has been an eager adopter of health care reform and has already set up its heath care exchange, by which residents can purchase their own insurance and get federal subsidies to afford it. That's largely because the city has long subsidized health care for the uninsured through its Healthcare Alliance, said Jack Meyer, a health economist at Health Management Associates.

"Now that they've rolled them into Medicaid under early adoption, they get a federal match on the money spent," Meyer said.

The city's uninsured rate for its population that earns up to 138 percent of the poverty line -- $31,809 annually for a family of four -- is 13 percent. That's far below Maryland's 25 percent and Virginia's 30 percent.

Virginia, meanwhile, has balked at the plan and is slow in putting the pieces in place for 2014. That state has strict eligibility requirements for Medicaid compared with D.C. and Maryland. As a result, many working adults earning minimum wage don't qualify and are uninsured, accounting for Virginia's higher rates among its low-income population, said George Washington University professor Lara Cartwright-Smith.

She said if Virginia does not expand Medicaid, the state's working poor will have to purchase insurance through the health exchange. But whether that will be affordable for those people "is unclear."

"Places that don't expand medicaid are really going to be hurting," Cartwright-Smith said.

Maryland has plans to expand its Medicaid program and is setting up its health exchange.