WASHINGTON — After knocking on 50 million doors and handling tens of millions of surveys, the Census Bureau on Tuesday announced that the official population of the United States is now 308,745,538.

The 2010 census also shows America's once-torrid population growth dropping to its lowest level in seven decades. The new number, based on the surveys taken on April 1, 2010, is a 9.7 percent increase over the last census, 281.4 million residents in 2000. But that's slower than the 13.2 percent increase from 1990 to 2000. And it's the slowest rate of increase since the 1940 census. That is the decade in which the Great Depression slashed the population growth rate by more than half, to 7.3 percent.

The Census figures will be used to reapportion the 435 House seats among the 50 states. The numbers trigger a high-stakes process wherein the dominant party in each state redraws the election map, shaping the political landscape for the next 10 years.

In Congress, the steady migration to the South and West should be a boon for Republicans, with GOP-leaning states led by Texas picking up House seats.

The most populous state was California (37,253,956); the least populous, Wyoming (563,626).

The state that gained the most numerically since 2010 was Texas (up 4,293,741 to 25,145,561); the state that gained the most as a percentage was Nevada (up 35 percent to 2,700,551).

Politically, Texas will gain four House seats due to a burgeoning Hispanic population and a diversified economy that held up relatively well during the recession. Other winners are GOP-leaning Arizona (1) and Florida (2).

States that lose seats are: Illinois (1), Iowa (1), Louisiana (1), Massachusetts (1), Michigan (1), Missouri (1), New Jersey (1), New York (2), Ohio (2), Pennsylvania (1).