It will be "like a Y2K New Year's Eve party for genealogists," Liesa Healy-Miller, a Framingham, Mass., genealogist, told The (Framingham) MetroWest Daily News.
The personally identifiable information, kept secret for 72 years, is to be released online by the National Archives and Records Administration, at 1940census.archives.gov, at 9 a.m. EDT, preceded by "an opening event live webcast" at 8:30 a.m.
The information is expected to offer insights into a country radically altered by the Great Depression, Annie Davis, an NARA education specialist in Waltham, Mass., told the newspaper.
The Depression, which began with the Wall Street crash of Oct. 29, 1929, brought about widespread high unemployment and poverty as industry, construction and agriculture came to a near-halt.
Roosevelt's economic recovery plan, known as the New Deal, created unprecedented economic programs focused on what historians later called "relief, recovery and reform."
Among the questions people were asked in the 1940 census was if they worked for one of the New Deal programs.
For the first time, they were also asked what their income was and if they had a Social Security number.
Census questions also included what language was spoken at home, whether a woman had been married more than once, where people lived five years earlier and the highest educational grade achieved.
NARA -- an independent federal agency charged with preserving and documenting government and historical records and with increasing public access to those documents -- has a rule it won't release personally identifiable census information until 72 years after it is collected.
The 1940 census date was April 1.
The 1930 census records, released 10 years ago, were made available on microfilm, available at participating libraries.
While the 1940 records will be immediately available to anyone with computer access, they won't be readily searchable by name until they're fully indexed, officials say.
FamilySearch.org -- the largest genealogy organization in the world, run by the Church of Jesus Christ of Latter-day Saints -- says it will release batches of searchable-by-name records, in collaboration with other genealogical organizations, as soon as each batch is transcribed and checked for accuracy.
Ancestry.com says it has a similar plan to convert the records into more easily usable formats.
No date has been set for when easily searchable information about all 132 million people surveyed by 120,000 census takers will be available.
Some 21 million people from the 1940 census are believed still alive, the U.S. Census Bureau says.