The mean center of the United States population is determined by the United States Census Bureau from the results of each national census. The Bureau defines it 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 on one person. More specifically, this calculation is called the mean center of population.
After moving roughly 600 mi (966 km) west by south during the 19th century, the shift in the mean center of population during the 20th century was less pronounced, moving 324 mi (521 km) west and 101 mi (163 km) south. Nearly 79% of the overall southerly movement happened between 1950 and 2000.
^The addition of Alaska and Hawaii to the union in 1959 contributed to moving the mean center of population about 2 miles (3.2 km) farther south and about 10 miles (16 km) farther west in the 1960 census.
The 20.7-mile (33.3 km) shift projected for the 2010–2020 period would be the shortest centroid movement since the Great Depression intercensal period of 1930–1940.