American Population Changes by County During the 20th Century

Michael Minn (michaelminn.com)

September 7, 2009

Over the 20th century, the population of the United States nearly quadrupled from 76.2 million in 1900 to 281.4 million in 2000. This page contains maps of population and population density changes over the decade by county that make it possible to observe population flows across and around the U.S. mainland.

Individual maps for specific years can be viewed by rolling your mouse over the year legend below animated images. Rolling your mouse over "Animate" (where available) causes the maps to be successively displayed as an animated time-series.

Population Density Changes by Decade

Population density (county population divided by county area) is a good metric for evaluating population in a way that makes it possible to compare and visualize counties fairly regardless of physical size. The changes in density over the decade show growth in the West and South that reflects a broader dispersal of population made possible by the automobile and suburbanization.


1900 - 1910 - 1920 - 1930 - 1940 - 1950 - 1960 - 1970 - 1980 - 1990 - 2000 - 2008 - Animate

Population Change by Decade

In contrast to the fairly clear national trends observed in the density map, mapping of the population change within individual counties during each decade gives a much more complex picture. Other than the depopulation of the plains states during the "Dust Bowl" drought in the 1930s and a surprising level of stasis during the 1980s, the changes in county population during the 20th century generally seem to be driven by regional and local factors that defy national generalization.


1900s - 1910s - 1920s - 1930s - 1940s - 1950s - 1960s - 1970s - 1980s - 1990s - 2000s - Animate

Population Changes 1980 - 2008

The maps below focus on cumulative population change during the 28 years from 1980 (the beginning of the "Reagan Revolution") and 2008. Increased agricultural consolidation as well as deindustrialization and globalization may be primary factors in a decline of population in the Appalacia, the midwestern rust belt, and the Great Plains. Gainers during this period were the coasts, the desert Southwest, and parts of the South (notably Florida).


1982 - 1984 - 1986 - 1988 - 1990 - 1992 - 1994 - 1996 - 1998 - 2000 - 2002 - 2004 - 2006 - 2008 - Animate

Mapping this period by population change rather than simple population growth more dramatically shows the population loss in the plains states, although the the reduction is overemphasized because of the already comparatively small population in the region.


1982 - 1984 - 1986 - 1988 - 1990 - 1992 - 1994 - 1996 - 1998 - 2000 - 2002 - 2004 - 2006 - 2008 - Animate

Metropolitan Statistical Area Contraction

The bubble map below shows the relative 2008 population of Metropolitan Statistical Areas (MSAs) within the boundaries defined for the 2000 census. MSAs are useful for observing the general population of metropolitan areas in a way that accounts for sprawl and negates the donut-hole effect of depopulated inner-cities. Population figures were obtained by performing a spatial join between the MSA areas and the counties comprising that MSA, with summation of population from all constituent counties.

Green bubbles represent areas that were as large in 2008 as they had ever been. Red bubbles represent areas that had a smaller population in 2008 than they had at some point in the 20th century. For example, the beleagured Detroit MSA had an estimated population peak of 4,499,091 in 2004 before dropping to 4,425,100 in 2008. The Cleveland MSA peaked at 2,153,598 in 1996 before dropping slowly but steadily to 2,088,291 in 2008.

By contrast, the largest MSA, NY/NJ/Long Island, increased in population steadily over the 20th century and had 19,006,798 estimated residents in 2008. New York County (the island of Manhattan) dropped in population steadily from an immigration-fueled peak of 2,762,522 in 1910 to a post-white-flight nadir of 1,428,285 in 1980 before beginning a slow rebound. However, the problems of the inner city and dispersion of the population to the surrounding suburbs masked otherwise consistent regional population growth.

Data

Population data and shapefiles for mapping were obtained from the U.S. Census Department website in early September 2009. The county level data joined with the shapefile can be downloaded HERE for further exploration. The shapefile columns are as follows: