Every ten years The U.S. Census Bureau announces the mean centre of the United States based on population figures from the latest census. Described thus:
the place where an imaginary, flat, weightless and rigid map of the United States would balance perfectly if all 308,745,538 residents counted in the 2010 Census were of identical weight.
As the Western States have become more populated, this location has progressed from east to west in a remarkably consistent manner. Starting from Chesterton, Maryland in 1790, the 2010 data now puts it near Plato, Missouri . Check out the precise change in location, at ten year intervals in this Google Map: