The population of the colonies that later became the United States increased steadily in the decades prior to, and including, the American revolution. The first decennial census, mandated in the U.S. Constitution, took place in 1790. Since that time, the natural increase, i.e. the excess of births over deaths, has been a constant contributor to population growth. The other factor, immigration, has ranged from negligible to large at various points in the nation`s history. The tendency in agricultural economies for early marriage and large numbers of children resulted in regular population growth during the decades preceding 1830, with only a small contribution from immigration.

After 1830, immigration began to grow again. Although the birth rate showed a decline, the net population growth rate remained high until after the Civil War. In the decade ending in 1870, population growth dropped below 30% for the first time in the nation`s history. Substantial immigration kept the population rising at 20% or more for each decade until 1920, when the effect of World War I reduced it to 14.9%. After a small rise in the next decade, the decade of the Great Depression gave America its lowest decadal increase ever at 7.2%.

Henry A. Wallace wrote in his book New Frontiers in 1934, that the end of population growth in the United States as in sight. "Today, immigration is mostly shut out. Our birthrate is decreasing. It appears that by 1950 our population will probably reach its peak, around a hundred and fifty million people, and then start declining."

Wallace was correct about the 1950 census, but otherwise missed the trend. In the postwar period, the "Baby Boom" reversed the decline. In recent years, the arrival of millions of immigrants from Mexico and other countries, along with tendency of Hispanic households to larger numbers of children, have been the major factors in continued population growth.

NOTE: New method for determining Urban/Rural designation is used in figures for 1950 and later.