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:
After moving roughly west by south during the 19th century, the shift in the mean center of population during the 20th century was less pronounced, moving west and south. Nearly 79% of the overall southerly movement happened between 1950 and 2000.
One occasional confusion is the misconception that the point splits the US population into two equal halves, such that half of Americans live east of the point, and the other half west of it, however, this is actually a property of the median center of US population, which is not weighted by geographic distance and lies in Gibson County, Indiana.