Genealogists are rightly excited about the 1940 census being released. It is available to everyone through the web site of the National Archives and Records Administration:
Unfortunately, the name index is a work in progress. You can see how much of your state has been done on the web site: www.familysearch.org/1940census . You go to the appropriate county and state, and then search the enumeration districts. The latter usually has some form of index by street. City directories, if available, can be a big help but it can be a slow process.
Efforts are being made to create a name index and, so far, the District of Columbia and Nevada have been done. (In 1940, even Cullman County had more people than the entire state of Nevada.) The 1940 census never had a soundex index. The federal census has been compiled roughly every ten years since 1790 for determining the population for purposes of apportioning the members of Congress. In 1885, a census was taken for the few states willing to help pay for it, such as Florida , to reflect their growth in population. The 1920 census was taken but was ignored by the then Republican Congress and President because it would have given the Democrats new districts as Americans were moving from the country to the cities in greater numbers).
Some of the census records, such as for Alabama in 1820, have been lost from before 1830. State censuses, tax lists, federal land records, voter records etc. can sometimes supplement or substitute for federal census records. The censuses for 1790 through 1840 are only lists of heads of households with statistical descriptions of each household, including counting members of the household who are older than the head of the household and people living in the household who are not family members. Indians were usually excluded from the censuses before 1870. Censuses began listing each free person starting in 1850. When a census is 72 years old, it is opened to the general public although anyone can purchase a copy of any federal census record where the person appears, even for 2010.
The census is intended to reflect the population of the United States on a specific day of the year. For 1940, it was April 1. On that day, the census takers began going door to door asking questions of people at home and, for those people not at home, of neighbors. It took weeks and weeks to compile the census and sometimes the information more accurately reflects the household on the day that the census taker visited than on April 1, 1940. If the person being interviewed was a member of the household, that fact is indicated on the census.
Aside from the usual questions about age, race, sex, place of birth, marital status, occupation etc., the 1940 census reflected the Great Depression and President Roosevelt’s New Deal. Special questions were asked about employment status, income, residence in 1935, participation in government work programs, military service etc. Five percent of the families had a longer supplemental questionnaire to provide the government with statistical data.
Bob Davis
The halfway point for indexing the 1940 U.S. census is fast approaching. 
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