When the 1940 Census is released on April 2, 2012, by NARA (National Archives and Records Administration), at first only the digital images will be made publicly available (free) at the official 1940census.archives.gov.
The 1940 U.S. Census Community Project, a joint initiative between Archives.com, FamilySearch.org, findmypast.com, is coordinating efforts to provide access to these digital images and start indexing them to make the ability to search online. If you are interested in volunteering to help index the images, visit The 1940 U.S. Census Community Project to sign up.
Last summer, I wrote about how to search for individuals in the 1940 census before indexes are available. See Tuesday's Tip ~ Getting Ready for the 1940 Census for details on how I did this to find out the enumeration districts I will browse through to find my parents.
The key websites you'll want to use to find your family members' enumeration districts (E.D.'s) are:
How to Access the 1940 Census "Quiz" at Steve Morse's One-Step website, where you'll have to know the street address your family member lived at.
Archival Research Catalog of the National Archives, where you'll want to search on "1940 Census Map [city] [state]" and look for the "digital copy available" icon at the left.
If you can't wait for the index to be completed, which could take six months, you'll want to do some preparation using these tools to narrow down where to look for your family members. Of course, this assumes you know the address where your family members are living. Good luck!