On April 2, 2012, the National Archives publicly released over 3 million images containing 1940 census responses. The information had been closed for a mandated 72 years, but is now available for free and online at http://1940census.archives.gov.
There were 132 million people living in the United States in 1940, Americans who had lived through the Great Depression and who would soon face world war on an unprecedented scale.
The U.S. government made a concerted effort to increase public participation in the census. Census Bureau marketing campaigns targeted the general public but also broke from tradition by specially reaching out to ethnic minorities, indigenous communities, and people of color. That year the census included standard questions from years past, but respondents were also asked for the first time about their income and whether they worked for New Deal agencies like the WPA, CCC, or NYA. Millions of people enumerated by the 1940 census are still living today.
The President, Mrs. Roosevelt and other members of the White House staff are listed in the District of Columbia enumeration district (ED) 1-74, which was taken on April 2, 1940. The information collected includes the age of the person, what state or country they were born in, their residence, employment information and their income for 1939. A full list of the 1940 Census questions can be found on the National Archives official 1940 Census website.
The full census information for the Roosevelts can be found here.
Surely there is something beneficial and important FDR did in one of the Aprils of his 12-year long presidency that the FDR Library could inform us about.