In addition, the report showed, median household income fell 2.3 percent between 2009 and 2010, from $50,599 to $49,445, adjusted to 2010 dollars.
At the same time, the number of people without health insurance increased from 49 million to 49.9 million, which the census deemed a statistically insignificant change.
Worse, 6.7 percent of Americans (20.5 million people) were living in deep poverty in 2010, defined as half the poverty rate or less. That is up from 6.3 percent (19 million people) in 2009.
"That's an all-time high" since records of deep poverty were first calculated in 1975, said Elise Gould, director of health and policy research for the Economic Policy Institute, a nonprofit, nonpartisan think tank in Washington that studies low-income people. She spoke Tuesday at a news conference on the census findings.
"I think it's astonishing to have so many Americans below $11,000 a year," she said.
Even more dire is the increase in the proportion of families living below 125 percent of the poverty line: from 18.7 percent (56.8 million) in 2009 to 19.8 percent (60.4 million) in 2010.
Women fared particularly poorly. Poverty climbed to 14.5 percent for women in 2010 from 13.9 percent in 2009, the highest rate in 17 years. Men's poverty was lower, increasing from 10.5 percent to 11.2 percent.
Census figures that showed that U.S. poverty would have been worse without antipoverty programs such as food stamps, federal earned-income tax credits, and unemployment insurance.
This safety net faces potential cuts and is fodder in presidential-year debates on how much help the government should offer Americans.
The census estimates that tax credits to the poor lifted 5.4 million families out of poverty.
In addition, census figures show that 3.2 million people were kept out of poverty by unemployment insurance.
