More than one in four immigrants came from Mexico. And 9.8 million school-age children or 18 percent of all those between ages 5 and 17 spoke a language other than English at home in 2000; the 1990 census placed the share at 14 percent.
Estimates from the wide-ranging Census 2000 Supplementary Survey released Monday come as lawmakers and advocacy groups debate how to shape policy on immigration and bilingual education.
The statistics on language spoken at home reflect youngsters who receive most of their formal education in English, but speak a second language with their families
Close to seven in 10 of those children spoke Spanish at home, and two-thirds of that group rated themselves as speaking English very well. Fluency declines as people get older, as 50 percent of those age 18 to 64 who spoke Spanish at home described themselves as fluent in English.
Meanwhile, the total foreign-born population made up about 11 percent of the country's household population of 273.4 million - the largeest percentage since the 1930s.
William Frey, a demographer with the Milken Institute think tank, said the survey data also lent support to 2000 census figures showing rapid minority population growth in states beyond California and New York.
Survey information was gathered separately from the 2000 census and provides estimates of demographic trends expected to be reflected in additional census data due out next year.
The survey also covers topics such as income and poverty, educational attainment, commuting times and fertility. It is not considered a substitute for the official 2000 census figures.
Much of the recent attention on the census from Congress and the White House has focused on figures that showed the Hispanic population grew 58 percent during the 1990s to 35 million. Hispanics now rival non-Hispanic blacks as the nation's largest minority group.
The new numbers offer more evidence of the diverse makeup of America's youth and show the need to expand bilingual education programs, said Lisa Navarette of the National Council of La Raza, the nation's largest Hispanic advocacy group.
She said the survey also helps to dispel the notion that children who speak Spanish at home have difficulty conversing in English.
A critic of bilingual education wondered why more than seven in 10 school-age children who speak Spanish at home did not rate themselves as speaking English very well.
"The figures should be closer to 100 percent," said Ron Unz, chairman of the Palo Alto, Calif.-based English for the Children, who successfully pushed a California ballot question in 1998 dismantling the state's bilingual education program.
Nearly 29 percent of the foreign-born population, or 8.8 million, came from Mexico, the survey estimated.
About 78 percent of the foreign-born from Mexico were not U.S. citizens, compared with half of those from Asia and 45 percent of native Europeans.
While the survey did not provide estimates of undocumented immigrants, an unofficial Immigration and Naturalization Service estimate places the number of illegal aliens in the country at roughly 7 million, with 5 million entering during the 1990s. Others have placed the illegal immigrant population to as high as 8.5 million.
The Bush administration is considering whether to give eventual permanent legal status to some undocumented Mexicans in the United States.
The supplementary survey was distributed to 700,000 households in 1,203 counties nationwide. It was administered at the same time as the 2000 census, but the census itself provides a broader picture of social trends because it was based upon forms mailed to 120 million households.
Unlike the census, the survey did not count people in institutions, such as prisons, college dormitories and nursing homes. Therefore, the estimates could be a little lower than the actual number, the bureau said.
The report is part of a Census Bureau test to see if such a survey done every year can replace the census long-form questionnaire sent out every 10 years.
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