Census Bureau Director Robert Groves says the figure represents an increase of 9.7 percent over the 2000 U.S. resident population of 281.4 million.
California is the most populous state with 37.2 million residents. Wyoming is the least populous with 563,626 residents.
Since the 2000 census, Texas gained the most people, up 4.3 million residents to 25.1 million. Nevada has gained the most residents as a percentage of its 2000 census count, growing 35.1 percent to 2,700,551.
The South and the West showed the strongest growth, although the Northeast and the Midwest also grew.