As we indicated in Census Records a census must be 72 years old before it is available to the public. In 2012 the 1940 US Federal Census became 72 years old and so on April 2, 2012 The U.S. National Archives and Records Administration (NARA) provided public access to the 1940 Census for the first time. The NARA provides free digital images of the Census.
The 1940 US Federal Census records contain important information about ancestors - like the names and ages of parents, children and siblings. In addition you can find information about an individual's education, birthplace, employment status, occupation and wage and salary information for 1939.
For a complete list of the information contained in the 1940 Census as well as the information that is included in all previous US Census years see Information in Census Records. Here you will find the information recorded for each census year from 1870 through 1940.
The National Archives (NARA) provides access to the images of the 1940 Census and these records can be read free of charge at 1940 Census Records.
When the census data in the 1940 Census was released in 2012 it was not indexed. So for example you couldn't enter an ancestor's name and find the page where his or her census records are located. However, Ancestry.com, FamilySearch, Archives.com, MyHeritage and other leading genealogy organizations have now indexed the 1940 Census records.
So for example you can go to Family Search - 1940 US Census where you can enter an ancestor's name and find his or her census records.
You can also organize your searches around the enumeration districts used in 1940. These districts refer to the area of a city or town that an enumerator (census taker) covered when asking the census questions. If you know where a person was living in 1940 then you can find the enumeration district and this will help you find that person in the Census.
NARA has provided a number of ways to find the 1940 Enumeration Districts at Online Public Access. Here you can search the 1940 Census Maps to find the name and number of the Enumeration District in which your ancestor lived.
Here is how to search for the Enumeration District - enter 1940 Census maps + the county + the state. Here is an example used by NARA - 1940 Census maps Sussex Delaware. When you receive your search results you will find a map and you should zoom into the map to find the street location where your ancestor lived. You will see the Enumeration District printed on the map - the first number is the county number and the second number is the enumeration district number within the county.
If you don't know where a person was living in 1940 you might look at the 1930 Census to find where the person was living in 1930. You might also try a Telephone or City Directory that was compiled around 1940 and World War II Draft records might also indicate where a particular family was living in 1940. You can also try looking at family records that might contain an address - letters and envelopes, newspaper clippings and passports as well as birth, marriage and death certificates.
Once you know the Enumeration District then you can find information about your ancestor in the online 1940 Census.
Enter the Enumeration District Number as requested by the NARA page and you will find the 1940 census records for that Enumeration District. Finally you can browse through the pages to find the street address where you ancestor lived and that is where you will find your ancestor's census record.