NEW YORK — It was a decade when tens of millions of people in the U.S. experienced mass unemployment and social upheaval as the nation clawed its way out of the Great Depression and rumblings of global war were heard from abroad.
Now, intimate details of 132 million people who lived through the 1930s will be disclosed as the U.S. government releases the 1940 census on April 2 to the public for the first time after 72 years of privacy protection lapses.
Access to the records will be free and open to anyone on the Internet — but they will not be immediately name searchable.
For genealogists and family historians, the 1940 census release is the most important disclosure of ancestral secrets in a decade and could shake the branches of many family trees. Scholars expect the records to help draw a more pointillistic portrait of a transformative decade in American life.
Researchers might be able to follow the movement of refugees from war-torn Europe in the latter half of the 1930s; sketch out in more detail where 100,000 Japanese Americans interned during World War II were living before they were removed; and more fully trace the decades-long migration of blacks from the rural South to cities.
Henry Louis Gates Jr., a Harvard University professor and scholar of black history who has promoted the tracing of family ancestry through popular television shows, said the release of the records will be a "great contribution to American society."
Gates, whose new PBS series "Finding Your Roots" begins March 25, said the "goldmine" of 1940 records would add important layers of detail to an existing collection of opened census records dating to 1790.
"It's such a rare gift," he said of the public's access to census records, "especially for people who believe that establishing their family trees is important for understanding their relationship to American democracy, the history of our country, and to a larger sense of themselves."
Margo Anderson, a census historian, said the release of the records could help answer questions about Japanese-Americans interned in camps after the outbreak of WWII.
"What we'll be able to do now, which we really couldn't do, is to take a look at what the Japanese-American community looked like on the eve of evacuation," said Anderson, a professor of history and urban studies at the University of Wisconsin-Milwaukee.
More than 120,000 enumerators surveyed 132 million people for the Sixteenth Decennial Census — 21 million of whom are alive today in the U.S. and Puerto Rico, according to the U.S. Census Bureau.
The survey contained 34 questions directed at all households, plus 16 supplemental questions asked of 5 percent of the population. New questions reflected the government's intent on documenting the turbulent decade, by generating data on homelessness, migration, widespread unemployment, irregular salaries and fertility decline.
Some of the most contentious questions focused on personal income and were deemed so sensitive they were placed at the end of the survey. Less than 300,000 people opted to have their income responses sealed.
In part because of the need to overcome a growing reluctance by the American public to answer questionnaires and fears about some new questions, the bureau launched its biggest outreach and promotional campaign up to that time, according to records obtained at the Franklin D. Roosevelt Presidential Library and Museum in Hyde Park, N.Y.
It opened its first Division of Public Affairs to blanket the country with its message, reaching out to over 10,000 publications and recruiting public officials, clergy and business owners to promote it.
Movie studios were enlisted to encourage their film stars to participate, including Cesar Romero, who later played the Joker in the Batman television series. A photograph of President Franklin D. Roosevelt taking the census also was used for the campaign.
The bureau also hired the managing editor of "Opportunity: A Journal of Negro Life" to galvanize support in the black community. However, studies in the 1940s revealed undercounts, including 13 