For the first time, racial and ethnic minorities make up more than half the children born in the U.S., capping decades of heady immigration growth that is now slowing.

New 2011 census estimates highlight sweeping changes in the nation's racial makeup and the prolonged impact of a weak economy, which is now resulting in fewer Hispanics entering the U.S.

"This is an important landmark," said Roderick Harrison, a former chief of racial statistics at the Census Bureau who is now a sociologist at Howard University. "This generation is growing up much more accustomed to diversity than its elders."

50.4% births minorities in July 2010-2011

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Minorities made up roughly 2.02 million of U.S. births between July 2010-2011. (iStock)

According to a U.S. census, minorities made up roughly 2.02 million, or 50.4 per cent of U.S. births in the 12-month period ending July 2011. That compares with 37 per cent in 1990.

In all, 348 of the nation's 3,143 counties, or one in nine, have minority populations across all age groups that total more than 50 per cent. In a sign of future U.S. race and ethnic change, the number of counties reaching the tipping point increases to more than 690, or nearly one in four, when looking only at the under age five population.

— The Associated Press 

The report comes as the U.S. Supreme Court prepares to rule on the legality of a strict immigration law in Arizona, with many states weighing similar get-tough measures.

"We remain in a dangerous period where those appealing to anti-immigration elements are fuelling a divisiveness and hostility that might take decades to overcome," Harrison said.

As a whole, the nation's minority population continues to rise, following a higher-than-expected Hispanic count in the 2010 census.

Minorities increased 1.9 per cent to 114.1 million, or 36.6 per cent of the total U.S. population, lifted by prior waves of immigration that brought in young families and boosted the number of Hispanic women in their prime childbearing years.

But a recent slowdown in the growth of the Hispanic and Asian populations is shifting notions on when the tipping point in U.S. diversity will come — the time when non-Hispanic whites become a minority. After 2010 census results suggested a crossover as early as 2040, demographers now believe the pivotal moment may be pushed back several years when new projections are released in December.

The annual growth rates for Hispanics and Asians fell sharply last year to just over 2 per cent, roughly half the rates in 2000 and the lowest in more than a decade. The black growth rate stayed flat at 1 per cent.

Of the 30 large metropolitan areas showing the fastest Hispanic growth in the previous decade, all showed slower growth in 2011 than in the peak Hispanic growth years of 2005-2006, when the construction boom attracted new migrants to low-wage work. They include Lakeland, Florida; Charlotte, North Carolina; Atlanta; Provo, Utah; Las Vegas; and Phoenix. All but two — Fort Myers, Florida, and Dallas-Fort Worth — also grew more slowly last year than in 2010, hurt by the jobs slump.

Latino population boom possibly peaking

Pointing to a longer-term decline in immigration, demographers believe the Hispanic population boom may have peaked.

The Latino population is very young, which means they will continue to have a lot of births relative to the general population," said Mark Mather, associate vice-president of the Population Reference Bureau.

"But we're seeing a slowdown that is likely the result of multiple factors: declining Latina birth rates combined with lower immigration levels. If both of these trends continue, they will lead to big changes down the road." 

William H. Frey, a demographer at the Brookings Institution who analyzed the census data, noted that government debates over immigration enforcement may now be less pressing, given slowing growth.

"The current congressional and Supreme Court interest in reducing immigration — and the concerns especially about low-skilled and undocumented Hispanic immigration — represent issues that could well be behind us," he said.

Births actually have been declining for both whites and minorities as many women postponed having children during the economic slump.