By Lena H. Sun
Washington Post Staff Writer
Wednesday, July 28, 2010; A13

New census data released Tuesday confirm a huge spread in the rate of uninsured from state to state and the big difference in impact that can be expected as a result of the health-care overhaul recently passed by Congress.

The statistics are for 2007 and show health insurance coverage by state and for each of the country's roughly 3,140 counties.

The numbers do not include the impact on millions of people who lost their jobs and health insurance after the recession began in December 2007.

The 2007 snapshot shows that Massachusetts, which has achieved near-universal coverage, had the lowest rate of uninsured people under age 65, about 7.8 percent. States with the highest rates of uninsured were in the South and West: Texas was at the top, with 26.8 percent, followed by New Mexico (26.7 percent) and Florida (24.2 percent).

In the Washington area, the District had the lowest rate of uninsured, about 11.9 percent, among the three jurisdictions. Maryland's rate of uninsured was 14.5 percent, and Virginia's was 15 percent. The data for the insured include those with public or private insurance.

The disparities are even greater at the county level, where Henry County, Iowa, and Plymouth County, Mass., tied for the lowest rate of uninsured in the country, about 6.6 percent of people under 65, with a margin of error of about 1 percent. By comparison, the 14 counties with the highest rates of uninsured were in Texas, with a nearly 50 percent uninsured rate in Kenedy County.

In the Washington region, Montgomery (14.7 percent) and Fairfax (15.1) counties had comparable rates for the number of uninsured; rates were higher for Arlington (19.3 percent) and Prince George's (20.2 percent) counties.

Under the new law, virtually all Americans will be required to buy health insurance by 2014 or pay a penalty tax. Administration officials estimate that the changes will lead to coverage for 32 million more people, starting in 2014. The law is aimed mainly at people who cannot obtain or afford coverage through a workplace, because their employer does not offer any or because it is too expensive -- or because they are unemployed or work for themselves.

The census summary is the only source for estimates of health insurance coverage status for every county. It combines survey data with population estimates and information from aggregated federal tax returns, the food stamp program, and Medicaid and Children's Health Insurance Program (CHIP) records.