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In this undated photo provided by the Franklin D. Roosevelt Presidential Library and Museum, staffers at the U.S. Census Bureau in Washington mark up a map for use in the 1940 census. The map shows approximately 147,000 enumeration districts for census-taking purposes and will ensure against overlapping activities of census takers, or enumerators, and also to avoid missing any territory. (AP Photo/Franklin D. Roosevelt Presidential Library)

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.