Census Bureau's Question & Answers: Population: Geographic Center
What is the geographic center of the U.S. population and how has it changed?
Answer:
"There are a couple ways of describing the geographic center of the U.S. population.:

1. Each decade, the Census Bureau calculates the mean center of population . The center is determined as the place where an imaginary, flat, weightless and rigid map of the United States would balance perfectly if all 281,421,906 residents were of identical weight.

In 1790, it was near Chestertown, Maryland.
In 1880, it was in Covington County, Kentucky.
In 2000, it was in Phelps County, Missouri.

2. Another measure is the median center of the population .

In 1880, it was in Miami County, Ohio.
In 2000, it was in Daviess County, Indiana..."