The nation's foreign-born population continued to grow over the past decade -- to almost 13 percent of the nation's 309 million people -- according to a new report by the U.S. Census Bureau. The agency also found that foreign-born residents live in households, on average, that are larger than native-born residents' and have more children under age 18.

Immigrants in the United States are estimated to number 40 million, according to the bureau's report released Thursday, which is based on the bureau's 2010 American Community Survey. That is the largest number recorded by the bureau, but its historical data show the foreign-born share of the nation's population has been higher: at nearly 15 percent in 1890.

"The size of the foreign-born population has changed considerably over the last 50 years," Elizabeth Grieco, chief of the Census Bureau's Foreign-Born Population Branch, told reporters in a news briefing. She said the immigrant share of the population in 2010 was 12.9 percent, compared with 5.4 percent, or 9.7 million people, in 1960.

She said most of the growth in the immigrant population over the decade occurred between 2000 and 2006. Immigrants made up 11.1 percent of the country's population in 2000.

David Dyssegaard Kallick, a researcher for the Fiscal Policy Institute, based in Manhattan and Albany, who has studied immigration trends on Long Island, said, "What we've seen overall is an increase in the immigrant population through the early 2000s to the mid-2000s, peaking around the time of the economic expansion." He added, "Immigration has certainly fallen off in the last three years," citing stepped-up "enforcement by the Obama administration, and the economy. As there are fewer jobs, there are fewer immigrants who come."

Immigrants made up 22 percent of New York's population in 2010, the census report said. New York was one of four states where more than half of the immigrant population resided. California, Texas and Florida were the others.

According to 2006-2010 American Community Survey data released December, 20.7 percent of Nassau County's population was foreign-born; in Suffolk County figure is 14 percent.

Steven Camarota, director of research for the Center for Immigration Studies in Washington, which supports immigration limits, focused on immigrants' higher poverty rate, 19 percent, versus 15 percent for the native-born population.

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"We are not talking about people who come and don't work," Camarota said of immigrants. "That's not what's happening.

"We're talking about people who work but have a hard time being self-sufficient, and then the taxpayer has to step in," he said, when immigrant families access noncash welfare programs, like food assistance or Medicaid, often through their U.S.-born children.

Kallick countered that "having a lower income doesn't mean you're a drag on the economy. Immigrants are contributing to the economy and are often underpaid in doing so."