Before and After 1940: Change in Population Density

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County-level population change for the 1930s differed from the 1920s or the 1940s, as shown in this set of three maps. In the 1920s, a number of predominantly rural counties in the nation's eastern half saw declines in population and population density, often reflecting outmigration to cities. During the 1930-1940 decade the pattern reversed, with population and population density declines primarily located in the Great Plains. Between 1935 and 1940, 12 percent of the population moved to another county or state. This represented a lull in population movement that changed during and after WWII as geographic mobility increased in the U.S. For instance, between 1940 and 1947, 21.5 percent of civilians moved to different counties or states. In the 1940-1950 period, population density increased for the more urban and populous counties in the Northeast and Midwest, but declines were widespread in predominantly rural counties.

SOURCE: Maps are based on decennial census data 1930 to 1950. National migration figures quoted in the text are from the 1940 decennial census and the 1947 Current Population Survey.

NOTE: County boundaries are based on 2010 geography, to ensure comparability between decades. For counties in which there have been changes in extent between 1920 and 2010, decennial census data are used as the basis for estimates of historical populations. Data values were rounded to the nearest whole number before classing.

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