WASHINGTON - Hispanics accounted for more than half of the U.S. population increase over the last decade, exceeding estimates in most states as they crossed a new census milestone: 50 million, or 1 in 6 Americans.

Meanwhile, more than 9 million Americans checked two or more race categories on their 2010 census forms, up 32 percent from 2000, a sign of burgeoning multiracial growth in an increasingly minority nation.

The Census Bureau on Thursday released its first set of national-level findings from the 2010 count on race and migration, detailing a decade in which rapid minority growth, aging whites and the housing boom and bust were the predominant story lines.

Analysts said the results confirmed a demographic transformation under way that is upending traditional notions of racial minorities, political swing districts, even city and suburb.

"These are big demographic changes," said Mark Mather, an associate vice president at the nonprofit Population Reference Bureau. "There is going to be some culture shock, especially in communities that haven't had high numbers of immigrants or minorities in the past."

"By 2050, we may have an entirely new system of defining ourselves," he said.

According to data released Thursday, Americans continued their decades-long migration to fast-growing parts of the Sun Belt. Their move to big states such as California and Texas as well as fast-growing Mountain West states pushed the nation's mean center of population roughly 30 miles southwest to a spot near the village of Plato, Mo.

African-Americans in search of wider spaces increasingly left big cities such as Detroit, Chicago and New York for the suburbs, typically in the South. Both Michigan and Illinois had their first declines in the black population since statehood as many of their residents opted for warmer climes in the suburbs of places such as Atlanta, Dallas and Houston.

The smaller numbers were a surprise to some city officials, including New York Mayor Michael Bloomberg, who questioned the census count of 8.2 million for his city and suggested immigrants may have been missed.

Census director Robert Groves said the agency had not yet received any formal complaints about the census count and that overall indicators showed high accuracy in 2010 compared to 2000.

After initial fears of low participation, the 2010 count of the Hispanic population came in 900,000 higher than expected, matching or surpassing census estimates in 37 states, according to the Pew Hispanic Center, a nonpartisan think tank.

Many of the biggest jumps were in the South, including Alabama, Louisiana, North Carolina and Louisiana, where a small but fast-growing Hispanic population was fueled by immigrants during the housing boom.

Multiracial Americans now make up 2.9 percent of the U.S. population, a steadily growing group - even if it did not include President Barack Obama, who identified himself only as African-American on his census form. Obama's mother Ann Dunham, a white woman from Kansas, married his father, the Kenyan native Barack Obama Sr.

The vast majority of multiracial Americans lived in California, Texas, New York and Hawaii. The most numerous race combinations were white-American Indian or Alaskan Native, white-black and white-"some other race." In some cases, white Hispanics may be opting to list themselves as multiracial in the "some other race" category, which would put the actual number of multiracial Americans lower than the official tally of 9 million.

In all, racial and ethnic minorities made up about 90 percent of the total U.S. growth since 2000, part of a historic trend in which minorities are expected to become the majority by midcentury.

"Hispanics and immigrant minorities are providing a much needed tonic for an older, largely white population which is moving into middle age and retirement," said William Frey, a demographer at the Brookings Institution who analyzed many of the census figures. "They will form the bulk of our labor force growth in the next decade as they continue to disperse into larger parts of the country."

Among census findings:

-The number of non-Hispanic whites, whose median age is now 41, edged up slightly to 196.8 million. Declining birth rates meant their share of the total U.S. population dropped over the last decade from 69 percent to roughly 64 percent.

-In about 10 states, the share of children who are minorities has already passed 50 percent, up from five states in 2000. They include Mississippi, Georgia, Maryland, Florida, Arizona, Nevada, Texas, California, New Mexico and Hawaii.

-Asians grew by 43 percent over the last decade. They were tied with Hispanics as the fastest growing demographic group. For the first time Asians also had a larger numeric gain than African-Americans, who remained the second largest minority group at 37.7 million.

The race figures come as states in the coming months engage in the contentious process of redrawing political districts based on population and racial makeup. The new political maps - which will also change each state's electoral votes- will take effect by the 2012 elections.

Many of the states in the South and West that are picking up House seats are Republican leaning, such as Texas and Florida. But most of their growth is now being driven largely by Hispanics, who tend to vote Democratic, which could put those regions in play.

In Texas, which picks up four House seats, the chair of the state Senate's redistricting panel has acknowledged that at least one House seat in north Texas could be a "minority or Hispanic influence district." Republicans are also rejecting the notion they can't appeal to Hispanics, who accounted for two-thirds of the state's population gains from 2000 to 2010.

"Our legislators represent all their constituents," said Texas Republican Party spokesman Chris Elam. He and others noted that the party picked up - narrowly - two heavily Hispanic congressional seats from Democrats in South Texas.

In New Jersey, Republicans are forming an unusual alliance with some Hispanics, who just surpassed African- Americans as that state's largest minority group. Both groups are looking for a political map - in this case, involving legislative districts - that offers a more competitive edge.

New Jersey must have its map completed by April 3, with legal challenges all but certain to follow.

"For us, it's not about parties, it's about whether Latinos are going to have Latinos in the Statehouse," said Martin Perez, president of the Latino Leadership Alliance of New Jersey, who said he has met with Republicans.

In large metropolitan regions, U.S. suburbs are becoming more politically competitive because of their fast growth and changing demographics, said Robert Lang, a demographer at the University of Nevada-Las Vegas. He noted that minorities are increasingly moving from cities to nearby suburbs, while more conservative whites living in far-flung suburbs known as exurbs were moving closer to cities due to a spike in gas prices and the housing bust.

"That's the new contested space," Lang said, noting that Democrat Obama was able to win many suburban areas in 2008 before Republicans reclaimed much of the turf in the 2010 elections. "They grew the fastest in the last decade without resolving which way they will vote."

According to census, the 10 fastest-growing cities over the last decade were actually suburbs of major metropolitan areas. They included Lincoln, Calif.; Surprise, Ariz.; and Frisco, Texas, all of whose population more than tripled since 2000.

In all, U.S. metropolitan areas grew more than 10 percent over the last decade. It was also home to a record share of 83.7 percent of the U.S. population, with much of the growth in suburban areas.

"We expect this to continue," Groves said.

Associated Press writers Jay Root in Austin, Texas, and Beth DeFalco in Trenton contributed to this report.

Online: www.census.gov