The United States is the third largest country in the world with a population of more than 325 million, according to US Census Bureau. Where a child is born every 8 seconds, and a person dies every 12 seconds .. In addition to the Indians who They were already living on the continent, and the US population was built on immigration from other countries. Despite recent moves to close the US border to new refugees and immigrants, a new immigrant is moving to the states United every 33 seconds, according to the Bureau of Statistics.