The number of U.S. residents without health insurance soared to a record high last year as employment-based coverage plummeted, the U.S. Census Bureau said Thursday.

The number of uninsured in 2009 hit a record 50.7 million, up from 46.3 million in 2008, while the percentage of Americans without coverage climbed to 16.7% in 2009 from 15.4% a year earlier, the Census Bureau said.

Correspondingly, the number of people with health coverage dropped to 253.6 million last year from 255.1 million the previous year, which the Census Bureau said is the first time the number of insured declined since it began tracking health insurance coverage in 1987.

The percentage of people covered through employer-sponsored plans fell to 55.8% in 2009 from 58.5% in 2008, also a record low.

Conversely, the percentage of people covered through government programs increased, though that did not entirely offset the decline in employment-based coverage.

For example, the percentage of the population covered by Medicaid—the federal-state program for the poor—rose to 15.7% in 2009, up from 14.1% the previous year; and the number of people enrolled in Medicaid jumped to 47.8 million from 42.6 million. Those figures also are records.

On the other hand, the percentage and number of people enrolled in Medicare remained nearly steady in 2009 vs. 2008. In 2009, 43.4 million people were enrolled in Medicare. That was 14.3% of the population, about the same as 2008.

The decline in employment-based coverage came amid the worst economic downturn since the Great Depression. The unemployment rate topped 10% in 2009, with millions of employees losing their health insurance coverage. While Congress last year passed legislation in which the government paid 65% of COBRA health insurance premiums for laid-off employees, not everyone could afford to pay 35% of the premium.

At 5%, Massachusetts had the lowest uninsured rate—averaged over 2008 and 2009—of any state, according to the Census Bureau. That is the result of a 2006 law that created a program in which the state subsidizes health insurance premiums of the low-income uninsured, imposes penalties on employers not offering coverage and assessments on individuals without health insurance coverage—except those who can prove that affordable coverage was not available and those who obtain special waivers.

On the other hand, Texas had the highest state uninsured rate at 25.6%.

The U.S. Census Bureau report, “Income, Poverty and Health Insurance Coverage in the United States: 2009,” is available at www.census.gov.