The increases in areas that experienced little diversity until this decade intensify the uproar over immigration. Forty-one states have enacted 171 laws this year aimed at illegal immigrants. About 100 communities have proposed similar ordinances; 40 have been enacted.

"We're seeing new immigrant minorities coming in to areas that haven't had very much minority populations or immigrant populations," says William Frey, demographer at the Brookings Institution. "It put immigration on the front burner politically. It scared a lot of people."

The number of Hispanics has soared since 2000 in counties such as Paulding near Atlanta, Kendall on the western edge of Chicago, and Stafford, Prince William and Loudoun in Virginia, outside Washington.

None of the traditional immigrant gateways, including Los Angeles, Chicago and New York, remains among the fastest-growing Hispanic centers.

The Hispanic population in Pennsylvania's Luzerne County, two hours north of Philadelphia, nearly tripled since 2000, the fourth-fastest increase among large counties. Luzerne is home to Hazleton, which enacted a law last year that would have fined landlords who rented to illegal immigrants and suspended licenses of companies that hire them. A federal judge last month ruled the law unconstitutional.

Immigrants who resettled in the USA in the 1990s typically moved from California to escape that state's recession, says Jeffrey Passel, demographer at the Pew Hispanic Center. They flocked east to jobs in poultry and meatpacking plants. Then the housing boom happened.

"Immigrants who were coming in no longer were going first to California," he says. "This is a very fast turnaround. It accelerated and it's just continuing. … What causes the friction is the rapid change much more than the absolute number."

Not all the changes in the July 1, 2006, county estimates are caused by immigration, but they're a strong indicator of where immigrants settle. Births and moves from other parts of the USA add to the growth.

The high birthrate among Hispanics accounted for more than half the growth in Hispanics this decade, according to Kenneth Johnson, demographer at the University of New Hampshire's Carsey Institute.

As young Hispanics settle in places where the aging population is largely white, the generation gap widens, says Peter Morrison, demographer at the RAND Corp. In Philadelphia County, for example, 14% of whites are 65 and older, and 5% of Hispanics are.

"It's affecting school budgets and creating new needs that impinge directly on local taxpayers," he says. "How will the newcomers in these non-traditional gateways be transformed into productive workers and taxpayers? … The frictions will be most palpable at the local level."

The Census data show that diversity is increasing in more parts of the country. In 303 counties — nearly one of 10 — the share of whites has slipped below 50%. Eight more counties joined the list since 2005, and 205 others are nearing the mark with more than 40% minorities, nearly all in the South and West.

"We'll be able to see how well America can adapt to multiethnic populations," Frey says.