The urban proportion of the total U.S. population has risen steadily since the first Census in 1790. On a national plane, movement toward cities is a form of population aggregation, a centripetal movement of people. But, from very early days until the present, cities have grown in population by expanding outward. Hence, at the scale of the city or metropolis, the population shift is one of disaggregation, a centrifugal movement. These twin movements -- population concentration on a national scale and population decentralization on a metropolitan scale -- have been under way for many decades and seem likely to continue indefinitely.
Young people have migrated from farms to cities ever since our nation began. In earlier decades, this was the primary way that cities grew, for many had birthrates too low to have produced much growth on their own. For a long time, only part of the rural surplus of young people migrated, and rural populations also grew. But after World War I, approximately the full surplus of young rural people migrated to cities. Since World War II, the pace of rural-urban migration has so stepped up that more than half of all counties in the United States lost population during the decade of the 1950s. In many other counties, rural areas also lost, but the gain in the major settlements offset the rural loss. Some of the counties that lost population in the 1950s had also lost it in the 1940s and earlier decades; many of these same counties were losing population in the 1960s. A vast emptying-out of the more rural parts of the United States is in process. On the whole, the rate of migration to the cities seems to have slowed down in the later 1960s. In any case, its contribution to urban population growth has declined in relative importance, largely because the size of the rural population is now too small to contribute a continuing massive migration to the cities.
In some areas, especially near large cities, the rural nonfarm population is on the increase, but these new rural residents are really urban in their employment, their life styles, and their outlook. They simply live a little farther out than the suburbanite.
At the same time, the cities and the suburbs have acquired a demographic momentum of their own, which will lead to further increases in total urban popu