According to the Census Bureau:
Tracking the mean center of population tells a story of the nation's growth, conflicts, and social change. This interactive map from the U.S. Census Bureau shows the shifting mean center of population over time:
Today's mean center is in Texas County, Missouri - more than 1,000 miles from the first recorded center in Kent County, Maryland (1790). Some of the biggest shifts over time show the nation's development, and at times, growing pains.
Major shifts over time:
1790: First mean center is calculated as falling about 23 miles east of Baltimore, MD.
1810: The Louisiana Purchase (1803) doubled the land area of the nation, and the mean center shifted into Virginia.
1860: The center shifted by more than 80 miles (biggest shift on record) thanks to rapid growth in the nation's western states, driven in large part by the Gold Rush.
1870: Just ten years later the mean center of population experienced it's biggest shift to the north, as Northeastern and Midwestern cities experienced rapid post-Civil War growth as people fled the war-ravaged South. Also during this time Alaska became a U.S. territory (1867).
1920: The smallest shift on record was between 1910 and 1920. The nation's current territory had already been acquired, slowing the rate of westward expansion. The Northeast and Midwest saw large inflows of international migrants. And last, but certainly not least, there was substantial migration of black/African American population out of the South and into the Northeast and Midwest, precipitated by the intense racism that spawned the Jim Crow laws.
1950: After six decades in Indiana (the longest in any one state), the center finally crossed state lines into Illinois.
2010: The center has its biggest recorded shift to the south, as Georgia, Florida, North Carolina, South Carolina, and Texas record rapid population growth.