This report consolidates U.S. Census information from 1900-2000 to illustrate population changes over the 20th century. The population more than tripled, from 76 million in 1900 to 281 million in 2000. It grew increasingly metropolitan each decade. In 1900, half of the population was under 22.9 years old. By 2000, half of the population was over 35.3 years old. During the century, the population over age 64 increased tenfold. The country's gender composition shifted from majority male to majority female around midcentury. From 1900-2000, the number of non-southern states with populations of at least 10 percent races other than White increased from 2 to 26, reflecting the spread of diversity nationwide. From 1980-2000, the Hispanic population more than doubled. By 2000, California, Hawaii, New Mexico, and the District of Columbia had predominantly minority populations. Before 1950, over half of all occupied housing units were rented. By 1950, homeownership became more prevalent than renting. At the end of the 20th century, householders who were Black, Hispanic, or two or more races were more likely to rent than own their homes. In 1900, the most common household contained seven or more people. From 1940-2000, it contained two people. Between 1950-2000, married couple households declined from more than three-fourths of all households to just over one-half. (SM)