According to the Population Reference Bureau, each 100 million in U.S. population growth “has been added more quickly than the last. It took the United States more than 100 years to reach its first 100 million in 1915. After another 52 years, it reached 200 million in 1967. Less than 40 years later, it is set to hit the 300-million mark. Within another 37 years, we are projected to pass 400 million.” According to PRB, natural increase (excess of births over deaths) accounts for about 60% of U.S. annual population growth — a relatively high rate of increase compared with other developed countries. Immigration accounts for the remaining 40%. Read more