The number of adults sharing households with family members or other individuals jumped 11.4 percent between 2007 and 2010, the report said.
Overall, such living arrangements accounted for 22 million households in 2010 -- or 18.7 percent of all U.S. households, compared with 17 percent in 2007.
Young adults were the most likely to double up, the report said, accounting for more than half of those who moved in with family members or friends. Between 2007 and 2010, the number of adult children who lived in their parents' homes increased by 1.2 million to 15.8 million.
Those between the ages of 25 and 34 made up two-thirds of that increase, underscoring a prime reason for a broader slowdown in household formation that economists call both a symptom and a cause of the nation's continued economic doldrums.
Economists estimate that there are more than 2 million fewer occupied homes in the country than there would have been had Americans continued forming households at the rate they did before the recession. The slowdown has lowered demand for housing as well as for furnishings and appliances, placing a further drag on the economy.
"Although reasons for household sharing are not discernible from the survey, our analysis suggests that adults and families coped with challenging economic circumstances over the course of the recession by joining households or combining households with other individuals or families," said Laryssa Mykyta, a report co-author and a Census Bureau analyst.
The report added that such moves proved beneficial, with many Americans escaping poverty by sharing homes with families or friends.
The poverty rates for shared households were lower than for other households, although the adults who made up those households individually had high rates of personal poverty, which are defined by federal guidelines.
That was especially true for young adults. Those who lived with their parents had a poverty rate of 8.4 percent, but that figure included the entire household in calculating income. If the poverty status was determined using solely individual incomes, the poverty rate for those doubled-up young adults would have been 45.3 percent, according to the Census Bureau.
"It is difficult to assess the precise impact of household sharing on economic well-being," Mykyta said. "But the higher personal poverty rates for adults heading shared households suggests that this group has fewer individual resources than their counterparts."
Overall, 27.7 percent of adults -- 61.7 million people -- were doubled up in households in 2007, a number that rose to 69 million, or 30.1 percent, in 2010.
The Census Bureau defines "doubled up" households as those that include at least one "additional" adult -- a person 18 or older who is not enrolled in school and is not a spouse or live-in partner.
Americans were most likely to double up with other family members, the report found. In 2010, adult children accounted for 46 percent of those who doubled up, while parents who moved in with their adult children made up another 13 percent. Siblings, grandchildren and other relatives accounted for nearly 23 percent of those who doubled up, the report said.
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