California remains the biggest state with nearly 34 million residents, but Texas has ousted New York to move into second place.
The United States Census Bureau has announced that the country's population has grown to more than 281 million - a rise of more than 13% since the last count 10 years ago.
"Never have we been so diverse, never have we been so many and never have we been so carefully measured," said census director Kenneth Prewitt as he announced the main results at a news conference in Washington.
Coming so soon after the most tighly contested election in decades, the census figures will be keenly scrutinised by the political parties.
Undercounted
In simple terms, the US population now stands at 281.4 million, but the interest, and possibly the devil, are in the detail.
The main areas of growth are in the south and west - spurred in large part by an increase in Hispanics and a movement of people to economic growth areas such as Atlanta and Las Vegas.
California remains the biggest state with nearly 34 million residents, but Texas has ousted New York to move into second place.
What this means in political terms is a reallocation of seats in the House of Representatives; for example, Arizona, Texas, Florida and Georgia have all gained two sets, while New York and Pennsylvania have lost two.
Given the tightness of November's presidential and congressional elections, Democrats and Republicans are bound to examine the census figures minutely.
The allocation of federal and state funds also depends largely on the census results.
Civil rights groups have anxiously awaited the survey, arguing that in previous years the census has undercounted people from minority groups who they say are already under-represented in government.
The Census Bureau admits some people will have been missed, but a clearer picture will only emerge in March when more detailed statistics are released.