Updated

America hit a demographic milestone last year, with new census figures showing for the first time more than half the children born in the U.S. were minorities.

That percentage just barely eked over the halfway mark, with minorities making up 50.4 percent of U.S. births in the 12-month period ending July 2011. But it marks a steady trend -- minorities represented 37 percent of births in 1990.

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 percent to 114.1 million, or 36.6 percent 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.

The numbers also serve as a guide to where taxpayer dollars could be going in the coming decades. With minority populations growing faster than white populations, robust minority population centers are sure to increase in electoral heft in the coming decades.

"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."

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 above 2 percent, roughly half the rates in 2000 and the lowest in more than a decade. The black growth rate stayed flat at 1 percent.

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

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.

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.

In all, 348 of the nation's 3,143 counties, or 1 in 9, have minority populations across all age groups that total more than 50 percent. 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 1 in 4, when looking only at the under age 5 population.

According to the latest data, the percentage growth of Hispanics slowed from 4.2 percent in 2001 to 2.5 percent last year. Their population growth would have been even lower if it weren't for their relatively high fertility rates -- seven births for every death. The median age of U.S. Hispanics is 27.6 years.

Births actually have been declining for both whites and minorities, as many women postponed having children during the economic slump. But the drop since 2008 has been larger for whites, who have a median age of 42. The number of white births fell by 11.4 percent, compared with 3.2 percent for minorities, according to Kenneth Johnson, a sociologist at the University of New Hampshire.

Asian population increases also slowed, from 4.5 percent in 2001 to about 2.2 percent. Hispanics and Asians still are the two fastest-growing minority groups, making up about 16.7 percent and 4.8 percent of the U.S. population, respectively.

Blacks, who comprise about 12.3 percent of the population, have increased at a rate of about 1 percent each year. Whites have increased very little in recent years.

The Associated Press contributed to this report.