In this photo provided by the Library of Congress, Prints & Photographs Division, a poster for the 1940 Census is shown. 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/Library of Congress, Prints & Photographs Division)
The 1940 census records were released Apr. 2, with more than 21 million people alive in the U.S. and Puerto Rico.