I don't know when, but here are some suggestions for where...
The geographical center of the lower 48 states lies outside of Lebanon, Kansas, in the middle of a hog farm.
The geographical center of all 50 states is located 17 miles west of Castle Rock, South Dakota.
The geodetic center of the U.S. is found approximately 42 miles south of Lebanon, Kansas. (Note: A geodetic survey makes corrections to account for the curvature of the Earth.)
The geographical center of the lower 48 states lies outside of Lebanon, Kansas, in the middle of a hog farm.
The geographical center of all 50 states is located 17 miles west of Castle Rock, South Dakota.
The geodetic center of the U.S. is found approximately 42 miles south of Lebanon, Kansas. (Note: A geodetic survey makes corrections to account for the curvature of the Earth.)