FROM AN ESTIMATED 4,600 white inhabitants in 1630, the country’s population grew to a total of more than 308 million in 2010. It is important to note that the U.S. census, first conducted in 1790 and the source of these figures, counted blacks, both free and slave, but did not include American Indians until 1860. The years 1790 to 1900 saw the most rapid population growth, with an average increase of 25 to 35 percent per decade. In addition to “natural” growth—birthrate exceeding death rate—immigration was also a factor in that rise, especially between 1840 and 1860, 1880 and 1890, and 1900 and 1910. The twentieth century witnessed slower growth, partly a result of 1920s immigration restrictions and a decline in the birthrate, especially during the depression era and the 1960s and 1970s. The U.S. population is expected to pass 340 million by the year 2020.