Data for "Resident Population" from 1900 to present are estimates as of July 1
Source: US. Bureau of the Census
US. Bureau of the Census, Resident Population in the Great Lakes BEA Region [BEAGLPOP], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/BEAGLPOP/, July 3, 2015.