America's Population Mid-Line, 1790–2020
Topic: Population & Society
In this chart: Second Layer
About this chart
The gold line splits the population in half at each census: half of Americans live east of it and half west. The ringed gold dot on it is the median center of population, where it crosses the line that splits the population north and south, and the gold trail behind it is the path that center has taken. The violet dot is the average center of population, with its own trail. The bars at the left show how far west of the line the average center sits at each census. Before 1880 the line is DataSlapper's calculation from county populations; from 1880 it is the Census Bureau's own figure. The map is the lower 48 states on an equal-area projection. The animation runs the record over twenty-five seconds, holds on the last census for three seconds, and loops. The scrubber under the chart marks each census and pauses on any of them.
Method
The mid-line is the north–south line with half of the population east of it and half west. Where it crosses the east–west line that splits the population in half north and south is the median center of population. From 1880 to 2020 the line is the US Census Bureau's own median center of population at each census, as the Bureau publishes it: for the 48 conterminous states through 1950, and for all states from 1960. The Bureau did not compute a median center before 1880. For 1790 to 1870 DataSlapper computed it the same way from county populations: every county's population at each census, from the Census Bureau's report Population of States and Counties of the United States: 1790 to 1990, each county placed at its center of population in the 2020 census, and the line drawn where the counties to its east hold half of the population. A county that was later divided or renamed is placed at the present-day county that holds most of it. Checked against the Bureau's own median centers from 1880 to 1950, this method falls within 8 kilometers east or west of them at every census. The violet dot is the Census Bureau's mean center of population, the average of everyone's position; far-off people pull the average, but the middle only moves when people cross it. The distance given between the two is measured east to west. DataSlapper compiled the series; every figure on the page is computed from the rows the page serves.
Data sources
- US Census Bureau — median centers of population, 1880–2020 (Centers of Population Computation for the United States 1950–2020, Table 2)
- US Census Bureau — mean centers of population of the United States, 1790–2020
- US Census Bureau — Population of States and Counties of the United States: 1790 to 1990 (1996), county populations 1790–1870
- US Census Bureau — 2020 county centers of population (where each county is placed, 1790–1870)
Data table
The median center of population of the United States at each census from 1790 to 2020 — the Census Bureau's own figure from 1880, DataSlapper's calculation from county populations before — with the Census Bureau's mean center of population and the east–west distance between them. The mid-line is the median center's line of longitude. Compiled by DataSlapper from the Census Bureau's centers of population and its county populations 1790–1870. These are the rows the chart draws.
Show all 24 rows
| Census | Median latitude | Median longitude | Source of the median | Mean latitude | Mean longitude | Mean west of the line |
|---|---|---|---|---|---|---|
| 1790 | 39.65174 | -76.29183 | county | 39.27500 | -76.18667 | 9.0 km east |
| 1800 | 39.64673 | -76.59592 | county | 39.26833 | -76.94167 | 29.7 km |
| 1810 | 39.67318 | -76.88159 | county | 39.19167 | -77.62000 | 63.4 km |
| 1820 | 39.61751 | -77.49973 | county | 39.09500 | -78.55000 | 90.3 km |
| 1830 | 39.62757 | -78.18690 | county | 38.96500 | -79.28167 | 94.2 km |
| 1840 | 39.75792 | -79.83064 | county | 39.03333 | -80.30000 | 40.3 km |
| 1850 | 39.87610 | -80.73569 | county | 38.98333 | -81.31667 | 49.9 km |
| 1860 | 39.98963 | -82.42550 | county | 39.00667 | -82.81333 | 33.3 km |
| 1870 | 40.00348 | -83.33513 | county | 39.20000 | -83.59500 | 22.3 km |
| 1880 | 39.95000 | -84.12000 | census | 39.06889 | -84.66111 | 46.4 km |
| 1890 | 40.04751 | -84.66694 | census | 39.19889 | -85.54806 | 75.5 km |
| 1900 | 40.05889 | -84.81694 | census | 39.16000 | -85.81500 | 85.5 km |
| 1910 | 40.12583 | -85.03333 | census | 39.17000 | -86.53889 | 128.9 km |
| 1920 | 40.19778 | -84.73334 | census | 39.17250 | -86.72083 | 170.1 km |
| 1930 | 40.19778 | -84.60973 | census | 39.06250 | -87.13500 | 216.3 km |
| 1940 | 40.07167 | -84.66973 | census | 38.94833 | -87.37639 | 232.2 km |
| 1950 | 40.00333 | -84.94750 | census | 38.80417 | -88.36889 | 294.0 km |
| 1960 | 39.94028 | -85.28333 | census | 38.59944 | -89.20972 | 338.0 km |
| 1970 | 39.79528 | -85.52861 | census | 38.46306 | -89.70611 | 360.4 km |
| 1980 | 39.31667 | -86.13750 | census | 38.13694 | -90.57389 | 384.9 km |
| 1990 | 38.96528 | -86.53139 | census | 37.87222 | -91.21528 | 408.1 km |
| 2000 | 38.75644 | -86.93074 | census | 37.69699 | -91.80957 | 426.2 km |
| 2010 | 38.472967 | -87.410365 | census | 37.517534 | -92.173096 | 417.4 km |
| 2020 | 38.297627 | -87.561798 | census | 37.415725 | -92.346525 | 420.1 km |
Updated 2020
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