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.
And, without food stamps, an additional 3.9 million people would be in poverty, 1.7 million of them children, according to Robert Greenstein, president of the Center on Budget and Policy Priorities, a nonprofit, nonpartisan group that studies policies affecting the poor.
These programs are "vital to the social and economic fabric of our country," said Mariana Chilton, professor at Drexel University's School of Public Health and a national expert on hunger. She said that last week's U.S. Department of Agriculture's hunger report showed that hunger levels in 2010 were around the same as 2009, proof that food stamps are helping.
"Ultimately, we need policies that invest in Americans rather than depleting it of jobs, and education, and resources," said Carey Morgan, executive director of the Greater Philadelphia Coalition Against Hunger.
What makes Tuesday's report even more grim is the expectation that no relief is in sight, EPI economist Heidi Shierholz said at the news conference.
"This is just another reminder of the huge impact of the Great Recession on the families of this country," she said. "I'm not surprised to see the deterioration. And unemployment is expected to stay very high for years to come."
That is especially bad news for people like Jennifer Markee, a 29-year-old single woman who lives with her boyfriend and five children in Frankford. She is part of the 9.9 percent of white people in poverty in 2010, up from 9.4 percent in 2009. (Black poverty went from 25.8 to 27.4 percent, while Hispanic poverty increased from 25.3 percent to 26.6 percent.)
Afflicted with epilepsy since birth, Markee's boyfriend cannot keep a job.
Meanwhile, Markee had to put her goal of becoming a dental hygienist on hold to care for a year-old son with severe asthma and a 10-year-son who is autistic.
The family receives welfare, food stamps, and Supplemental Security Income for various disabilities but is still left below the $33,270 poverty line for a family of seven.
"I know people would say, 'Why does she have five kids?' " Markee said. "Well, I don't believe in abortion, and I wasn't planning on having to not work to care for my sick kids. Walk a day in my shoes. Then you'd understand."
Contact staff writer Alfred Lubrano at 215-854-4969 or firstname.lastname@example.org. Read his blog, "The Joint Custodian," at www.philly.com/jointcustodian.
Staff writer Tom Avril contributed to this article.