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In this undated photo provided by the National Archives at College Park, William F. Arends, center, one of the more than 120,000 enumerators, returns to his dog sled after completing an enumeration near Fairbanks, Alaska for the 1940 Census. At right is musher Mike Agababa. Veiled in secrecy for 72 years because of privacy protections, the 1940 U.S. Census is the first historical federal decennial survey to be made available on the Internet initially rather than on microfilm. (AP Photo/U.S. Bureau of the Census, Dwight Hammack)

1940 census records released online

The 1940 census records were released Apr. 2, with more than 21 million people alive in the U.S. and Puerto Rico.