The Population Center of the US
The best statistic you've never heard of
The above map shows one of my favorite statistics: the mean center of population of the United States. Each triangle shows roughly the center of population in the United States according to the respective census. According to the US Census Bureau, the mean center of population can be defined as follows:
The concept of the center of population as used by the U.S. Census Bureau is that of a balance point. The center of population is the point at which an imaginary, weightless, rigid, and flat (no elevation effects) surface representation of the 50 states (or 48 conterminous states for calculations made prior to 1960) and the District of Columbia would balance if weights of identical size were placed on it so that each weight represented the location of one person. More specifically, this calculation is called the mean center of population.
Basically, the center of population shows the average place of residence for all Americans. Looking at the map through the years shows a few interesting population trends. The first, and obvious, is that the US population has moved steadily west through the decades. The advent and expansion of railroads is also clear, with the point moving west by large amounts during the middle of the 19th century.
Sometimes individual points tell a story. Within that westward surge across West Virginia and Southern Ohio, two points are noticeably closer to each other - the mean center of population for 1860 and 1870, which are only 54 miles apart. For the previous 30 years, the mean center of population had moved an average of 81 miles each Census. Then, from 1860 to 1870, it moved 54 miles. Then the center of population bounced back, moving 74 miles. What happened from 1860-1870? The Civil War, which temporarily stalled the unstoppable westward movement of Americans. Similar small movements are seen between 1910-1920 and 1930-1940. During the former, the United States fought in World War I and had several large financial recessions. The latter occurred during the Great Depression. In both cases, migration westward partially stalled.
The movement from 1910 to 1920 is also noteworthy: it’s the last time the US center of population moved north. The next 10 censuses (censei?) have all been in a southern direction. This can be partially traced to the invention and widespread adoption of air conditioning, which greatly improved year-round livability in the southern United States. It’s a relatively simple technology, but the ability to keep one’s home at a pleasant temperature regardless of outside heat has completely changed the calculus of living in a hot area.
In every census since World War II, the United States population has steadily moved both south and west. That trend, however, may be coming to an end. Compared to most of the 20th century, the 21st century has seen less movement. The 2010 and 2020 censuses show the same southwest direction of migration, but the shifts are much smaller. From 2000-2010 the population center only moved 25 miles, the smallest amount since 1930-1940. From 2010-2020 the population center moved a mere 12 miles, the smallest distance ever recorded. What’s going on?
I think part of the small movement from 2000-2010 can be credited to the Great Recession, which like previous economic downtowns reduced westward migration. The larger trend, however, is likely a resurgence of the American Southeast. Drawn by the low cost of living, Americans are moving by the millions to the Cotton Belt. The Carolinas, Texas, and Florida are all becoming popular draws for Americans looking to up sticks. At the same time, California’s population declined for the first time in 2020. Since California is so far west, its former attractiveness did a great deal to pull the mean center of population.
The net result could be an invisible yet important benchmark in American history: the end of net westward migration. There aren’t many trends in US history that, without exception, consistently go back to 1790. If the 2030 census shows a movement due south, or even to the east, it won’t mean it’s the death of California or the West Coast. Rather, it will signal the end of an era that goes back to the very first settlers. If the trend were to continue for decades, over the long term it could mean a subtle but ingrained new world where the south becomes the epicenter of American culture and economy.
Avid readers of this blog will know that I’m a big fan of thinking about both mean and median. The above map shows the progression of the US mean center of population. But what about the median center of population? While the mean shows the “balance point” of all people, the median shows the point around which an equal amount of Americans live. The map below shows the geographic center of the US (the square), the mean (the triangle), and the median center of population (the plus).
Why is there a difference? Imagine that every person who lives in Colorado decides to move to California. All 5.8 million people current Coloradans are well west of both the mean and median center of population. By moving farther west, those 5.8 million movers would pull the mean center of population to the west because it would require a recalculating of the “balance point” described in the Census Bureau’s definition above. The median center of population, however, would not move west at all, because the median is not influenced by outliers. This is clear from the map; the median center of population is in Indiana because it isn’t unduly influenced by the large distances of the West Coast (let alone Hawaii and Alaska).
What about the median center of population for each US State? I found the following map on Reddit:
This tells you a lot about each state. Indiana, for example, has a satisfying median population right in the middle of the state. This is also where Indianapolis, the state capital and largest city is located. Illinois, on the other hand, has a median center of population in the far northeast corner of the state. This is a testament to the relative size of the Chicago area, the population of which vastly exceeds the rest of the state. The median population center of New York is barely within the state, a testament to the size of New York City.
What will the future hold? Will the population shift to the east for the first time in US history in 2030? Or will 2010 and 2020 look like 1910 and 1920 - blips in an unstoppable westward trend the US has had since its founding? Time will tell.