WASHINGTON — The U.S. population on April 1, 2010, was 308,745,538, according to the decennial count conducted by the Bureau of the Census. The population was up 9.7% from 281,421,906 10 years earlier and up 24.2% from 248,709,832 20 years earlier. The most populous state was California (37,253,956), while the least populous was Wyoming (563,626). The biggest gainer since the 2000 Census was Texas, up 4,293,741 to 25,145,561, while the state that gained the most as a percentage of its 2000 Census count was Nevada, up 35.1% to 2,700,551. Regionally, the South and the West accounted for most of the population increase, 14,318,924 and 8,747,621, respectively. But the Northeast and the Midwest also grew, climbing 1,722,862 and 2,534,225, respectively. The U.S. Constitution requires the census to be conducted every 10 years, primarily for the redistribution of the 435 seats in the U.S. House of Representatives.