|1940 Enumeration District Map|
Federal law currently requires a 72 year waiting period before public release of census information, in order to protect personal information. However, of the 132 million people counted in the census, an estimated 21 million are still alive. Few of them, though, would have been adults at the time.
With the full blossoming of the Internet Age since the last census release, this one is being handled a bit differently. For the first time, information is being released directly by the National Archives online. Free access to the 1940 Census can be found here. There have been, and are, a few issues so far. For one thing, the response to the release was so great that the servers were overloaded on Monday, leaving many (including me) unable to access the images. That issue has since been resolved, and the site is now fully functional. Finding what you're looking for, though, is not yet as simple as it is for older censuses.
As of now, there is no name index for the 1940 Census, as there is for earlier ones. That means that you can't just type in a name and get taken directly to the appropriate census page. Instead, everything is grouped by enumeration district (ED). There are maps that show the EDs, like the one at the top of the post. Also, if you know the ED from the 1930 census, you can input that and it should show you the corresponding 1940 ED. Several groups, including Ancestry.com and FamilySearch.org are working on name indexing, so hopefully that will be in place in the near future. I believe they also have 1940 images available now, but I'm not sure of the extant of what they have.
Until the indexing is done, it'll take a little work to find who and what you're looking for in the 1940 Census (no, you don't have to admit if you're in it), but with all this new information, it's sure to be helpful. So, go and enjoy!