When the census is released on April 2nd, the digital copy will be viewable, free of charge, on personal computers or at NARA public access computers.
Not every researcher will be prepared to search the census. The 1940 census will be placed online by NARA, but it will not be searchable by variables such as names. If you are like me, you are so accustomed to searching the census online by surname that you have almost forgotten those squinty-eyed days of scanning reels of microfilms to find your ancestors in pages of street-by-street listings. While our computers will replace the dark rooms and microfilm readers, if we want to find our 1940 ancestors in a somewhat efficient manner online, we will need at least three important pieces of information: name, address, and enumeration district number (ED).
Researchers would be wise to begin collecting 1940 addresses now. Ask relatives for house numbers, street names, or, at least, neighborhood names. Go to local historical societies, libraries, and online genealogy databases to find 1940 city directories.The NARA site (link provided below) suggests additional sources of addresses: draft records, naturalization records, and the 1930 census (if your relatives did not change residences).
Once you have an address, you can obtain the ED number through NARA maps and resources online. Another useful site is Steve Morse's One Step page on the 1940 census. Steve Morse has a short, informative tutorial on his One Step site that can help you prepare to search the 1940 ceneus. Links to these handy sites are below.
I once found my grandmother's family in the 1915 NJ state census by beginning on page 1 and scanning each page. This feat (on a microfilm reader back in the days before Al Gore invented the Internet) took me two days and cost me a migraine. I will be better prepared with addresses and ED numbers in April!