The U.S. population almost quadrupled during the 20th century—at a growth rate of about 1.3% a year—from about 76 million in 1900 to 281 million in 2000. It is estimated to have reached the 200 million mark in 1967, and the 300 million mark on October 17, 2006. Foreign-born immigration has caused the U.S. population to continue its rapid increase, with the foreign-born population doubling from almost 20 million in 1990 to over 45 million in 2015, representing one-third of the population increase. Population growth is fastest among minorities as a whole, and according to the Census Bureau's estimation for 2020, 50% of U.S. children under the age of 18 are members of ethnic minority groups.