Why has it taken 72 years for this data to be released? The 1940 Census asked for information that was a little more detailed than today's census and since Title 13 of the United States Code restricts the availability of personally identifiable information from census records, it will only now become available due to expiring privacy protection.
Some interesting information can be gleaned from this data, including:
"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."
Full article over at GIS Lounge: 1940 U.S. Census Records Release Date Nears