Fifty years of growth and decline of subnational population in the United States

This study examines the growth and decline of the large metropolitan areas in the United States between 1960 and 2010 using census data.  In particular, the study focuses on metropolitan areas with a population of at least one million reached at any point during this 50 year period.  These large metropolitan areas accounted for less than 45 percent of the total US population in 1960, but almost 55 percent in 2010.  While the measurement of decennial changes in population might appear to be relatively straightforward, these trends are affected by the changing definition of metropolitan areas over time, changes in the actual boundaries of metropolitan areas from one census to another and the availability of data in a consistent manner.  The study therefore looks at trends in population growth and decline at a number of levels. 

First, it tracks trends in the population of large metropolitan areas without reference to the changing size of these metropolitan areas over time.  This approach provides a useful broad sweep, but it masks mergers and amalgamation of a metropolitan area with adjacent areas or the breakup of a metropolitan area.  This problem is partially solved by considering population densities as a second way of tracking population change.  Comparing population densities over time is helpful because it removes the issue of changing boundaries, but here again significant changes in land area between censuses tends to alter the true characteristics of the metropolitan area.  In addition to mergers and amalgamation, land area is also not constant due to changes in measurement technology and due to land being lost or reclaimed for natural or other reasons.  A third approach is to look at the large counties within metropolitan areas since the county boundaries change much less frequently than the boundaries of metropolitan areas and even when they do the changes are relatively small. 

Preliminary results show that the large metropolitan counties in the Northeast and the Midwest grew at the rate of five and four percent respectively between 1960 and 2010.  This contrasts sharply with the South and the West in which the large metropolitan counties grew 216 and 163 percentage points respectively over the same period.  Such massive regional differences deserve to be considered in detail.  The story at the county level reveals that five of the largest nine counties in the Northeast and two of the seven in the Midwest declined in population while even the counties registering the least growth more than doubled in the South and grew by over 60 percent in the West.

JEL Classification: I22, O10, O40