It remains to be seen how quickly there will be name access to the 1940 census. I am doing indexing on parts of it, and even with all the indexers working on them, it is only about 40 percent indexed at 2 months after the release. Still, that calculates out to the complete census being searchable by name within several more months.
So how is the census accessed at present? Those parts that have been indexed are accessible on several sites, including Ancestry.com and the free Familysearch.org.
Until all indexing is complete, one would have to browse by page through numerous pages of names. That's not too difficult if you seek people in a small area that is relatively unpopulated, but it could be very time consuming in larger, more thickly settled areas.
There is another concern, being that even as a indexer myself, I have seen enough errors in the indexing or rendering of names, that even when the indexes are available; it would be necessary to search creatively. By that, I mean first names, ages, country of origin or place of birth etc. I have seen in the 1940 census sheets the words Yugoslavia rendered as Jugoslonin; Wilhelmina as Whilhelmina; and Doris as Davis. The German name Krautwurst was rendered as Kraulvault, Kremtvaitt and even Huntarest. No index is perfect, and even if it was, there are people who just weren't counted. I have read that 5.4 percent were missed in 1940, inlciding over a million African Americans. An article in a Seattle newspaper (the Post-Intelligencer of May 21, 2012 ) estimated that 7.5 million folks were just plain missed.
But let's look on the bright side. Anything that could help people pinpoint addresses of family members during that period would be excellent. Is there anything "other" than city directories that could be used? So many towns did not have city directories -- and I'm sure lots of people were missed in the directories, as well. I, for one, am absolutely stuck right now, unable to use the census because I don't have an address for several of my families who were in a state of transit, coming out of the Depression. These were folks migrating from farm to city, small town to big city, state to state. Of course, finding individual addresses may be a lost cause and we just have to wait it out until the indexing is complete.
But there are other places to look for addresses of people in 1940. Several years ago I became aware of some rural registers that had been produced about 1940. Cataloging for it reads; "1940 rural register compass system" map (for Steuben County, New York It is 27 pages in length, and has a map folded into a pocket.) Why is this important? Because it gives the names and addresses of people who lived in what is then and now a very rural area. I bought the ones for the area near me and they are very useful.
There is also the ever resourceful Steve Morse, who has several helps on this web site, one being http://stevemorse.org/census/ed2040.php, which allows converting Enumeration Districts (EDs) between 1920, 1930 and 1940. He has more information at http://www.jewishgen.org/databases/stevemorse/census/quizremote.php, which says,
"The 1940 census is divided into EDs. The EDs are numbered. Within each state, each ED has a unique number. That number consists of two parts -- the first part specifying a region (typically a county) within the state and the second part specifying a district within that region. Once you have the ED number, you will be able to access the 1940 population census pages.
Keep in mind that the ED number will get you to the image of the first census page for that ED. Once you are there, you will need to step through the other images for that ED looking for the family that you are interested in."
He also has a wonderful pictorial help at http://stevemorse.org/census/xml1940edmaps.html, which allows you to set up a search and actually see the map on your computer.
Election or enumeration maps are in many libraries, Sadly, many of those worthy organizations have had to reduce their staff by as much as 50 percent over the last ten years, and while the remaining staff know what these maps are and where to find them in their collection, virtually none of them are cataloged in online catalogs, nor have been digitized. An enumeration district is a geographic area determined for purposes of taking the census. In one city there may be many enumeration districts, so once you enter a city, county, or state, you can narrow your results by entering street level information, or investigate Enumeration District maps, or descriptions.
Addresses may be found in city directory and phonebook listings. Some libraries have digitized these and made them available. Others have them but they must be used in person. Family correspondence and postcards are other sources of locations, and so are World War II military draft and service records. For those who died at the same address, death certificates may also provide address information. In fact, even naturalization petitions or declarations of intent filed close to 1940 would be helpful. Again, these may or may not be online to the public.
Other sources? Don't forget the obvious. Ask older family members. Interview living relatives and ask if they remember where the family lived in 1940. Check to see if there are old address books available for your family. Look in old address books or family documents. And if someone was in school at that time, see if you can find yearbooks, as these usually gave the addresses of the seniors, at least. And are there obituaries for family members that give that data?
Search a 1940 city directory if the address is in a city - particularly a larger city. Look at old county plat maps if the address was a farm or other land. Check also with a library, historical society, or the county assessor's office.
Eventually you will need to translate that address into an Enumeration District, or ED number that was used in 1940. In many small communities there was just one ED. In larger communities, an ED might have covered just a few blocks.
The National Archives has a helpful web site at http://1940census.archives.gov/getting-started/. And there are other web sites that would be useful to read and see if they help. One that I found is http://www.archives.com/experts/macentee-thomas/1940-census.html.
Best wishes until the index is complete! Oh, wait. As noted above it could make for interesting reading!