Many smaller areas, including Battle Creek, Mich., Ames, Iowa, and Corvallis, Ore., would shrink as well, according to population estimates to be released Thursday by the Census Bureau.
"Immigrants are filling the void as domestic migrants are seeking opportunities in other places," said Mark Mather, a demographer at the Population Reference Bureau, a private research organization.
Immigrants long have flocked to major metropolitan areas and helped them grow. But increasingly, native-born Americans are moving from those areas and leaving immigrants to provide the only source of growth.
The New York metro area, which includes the suburbs, added 1 million immigrants from 2000 to 2006. Without those immigrants, the region would have lost nearly 600,000 people.
Without immigration, the Los Angeles metro area would have lost more than 200,000, the San Francisco area would have lost 188,000 and the Boston area would have lost 101,000.
The Census Bureau estimates annual population totals as of July 1, using local records of births and deaths, Internal Revenue Service records of people moving within the United States and census statistics on immigrants. The estimates released Thursday were for metropolitan areas, which generally include cities and their surrounding suburbs.
There are about 36 million immigrants in the U.S. About one-third are in the country illegally. The Census Bureau, however, does not distinguish between legal and illegal immigrants.