In this undated photo provided by the Franklin D. Roosevelt Presidential Library and Museum, a Census Bureau staffer operates an electric tabulator at the U.S. Census Bureau. Data for the 1940 Census was collected by hand and transferred to punched cards which were then run through the tabulating machine. The tabulating machine printed the final calculation. (AP Photo/Franklin D. Roosevelt Presidential Library Museum)
The 1940 census records were released Apr. 2, with more than 21 million people alive in the U.S. and Puerto Rico.