Why is this data 72 years old? It's because these caches of Census data are always 72 years old when released. In an effort to protect privacy, it was decided that 72 years "balanced public release of federal records with the tradition of confidentiality," according to Vicki Glasier, of the U.S. Census Bureau, speaking to NPR.
In other words, it was decided that 72 years was long enough to ensure that most of the people in the Census will have passed away. With lifespans increasing, that's no longer such a sure thing.
Even if you can get to it, searching it, for now, will be cumbersome. Until a volunteer effort indexes the data, the only way to find someone is to find their "enumeration district," which is a geographic area assigned to each census taker.
However, with a team of online volunteers, the 1940 US Census Community Project hopes to index the information so that all of the information can be searched for free. The searchable index is expected to be ready by the end of this yes. Volunteers are welcome at http://the1940census.com.
Watch a behind-the-scenes video below.