Details in the 1940 Census You May Be Missing

The “Secret” Details in the 1940 Census You May Be Missing

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The 1940 census of the United States is a particularly exciting one for a number of reasons, and has been integral to many of us in our genealogy research. But there is a critical element of this massive family history resource that often gets overlooked.

Built into the 16th census of the USA was a brand new initiative — the collection of a statistical sample of information for the purpose of extrapolating demographic data for the entire US. This means that 5% of individuals listed in the census, or approximately 2 on every page, were asked additional questions about their lives.

Many researchers may already be aware of this–but for those who are new to census research, or who are simply not expecting the supplemental information, it can be easy to miss these “secret” details. 5% may not seem like a lot, but given that most families have multiple members listed on a page your chances of having a relation included are pretty good.

How do you know if your ancestor was selected to provide additional details?

Take a look at this census image below and you’ll see that entry number 42 has some additional text next to the number, “Suppl. Quest.” This denotes that the individual was asked the important additional questions.

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Where is this supplemental information found?

Scroll down to the bottom of the census page and you’ll see a section that says “Supplementary Questions.” Look for the correct slot for your ancestor, in this case 42, to find the additional information.


What additional details were collected? lists all of the questions that were asked on the 1940 census, including supplementary questions, on their website. The breakdown is below. To find information for other census years go here.

Supplementary Questions

  • Name
  • Person’s father’s birthplace
  • Person’s mother’s birthplace
  • Person’s mother or native tongue

To Veterans

Is this person a veteran of the United States military forces; or the wife, widow, or under-18-year old child of a veteran?

  • If so enter “Yes”
  • If the person is a child of a veteran, is the veteran father dead?
  • War or military service
    Enumerators were to mark “W” for World War I; “S” for the Spanish-American War, the Phillipine insurrection, or Boxer Rebellion; “SW” for both the Spanish-American War and World War I; “R” for peacetime service only; or “Ot” for any other war or expedition

Social Security: For persons 14 years old and over

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  • Does this person have a federal Social Security number?
  • Were deductions for federal Old-Age Insurance or railroad retirement made from this person’s wages in 1939?
  • If so, were deductions made from all, one-half or more, or less than one-half of the person’s wages or salary?
  • What is this person’s usual occupation?
  • What is this person’s usual industry?
  • What class of worker is this person?

For all women who are or have been married

  • Has this person been married more than once?
  • Age at first marriage
  • Number of children ever born

Where can I access the 1940 census records for free?

There are many places to find free census records online. We recommend FamilySearch. Find the search page for the 1940 census here.

The National Archives also hosts the 1940 census for free, but the records must be browsed though by location.

You can find more ideas for where to locate this resource and many other free genealogy records here.

Happy Searching!

Extra Census Tip: Always check the page directly before and after your ancestors’ entries on the census as you will often find relatives living nearby.

Also read The Ultimate Quick Reference Guide to the U.S. Census.

Image: US Department of Agriculture. “An enumerator visits a farmer for the 1940 Census. One of the fifty questions Americans were asked in 1940 was, ‘Does the person’s household live on a farm?'” Credit: Library of Congress, LC-USZ62-91199

23 thoughts on “The “Secret” Details in the 1940 Census You May Be Missing”

  1. Your example shows that supplemental questions were asked of a 5 month old (unless the indicator was not lined up with the correct person)…

  2. I was born in 1932 and lived at my grandfathers house in 1940 with my mother and sister and a couple of uncles. We are not on that census altho I have searched many times. The house was behind a 3 decker at 108 River street in Mattapan, a section of Boston, Massachusetts. My grandfather was Daniel L. Cushing, Mother was Madeline Cushing, my sister was Marianne Barrie and I was Joan Barrie at that time. Not sure which uncles were with us in 1940… Know that uncle Joseph Cushing was but not sure if Edward Cushing was. Any way of entering us for anyone searching? Thanks. Address was 108 River Street, Rear.

  3. I would love to know my great grandmother mom and dad’s name and her siblings. My great grandmother name: Martha Francis (Fannie -nickname) Russell (maiden) Young (married name) Martha was born in 1878 in Stgavsburg (spelling maybe wrong) Cass county, Missouri. She died at Marshall Hill, OK at home in November 27, 1943. She married a man by the name of James Henry Young and they married in 1894. If anyone knows about this family and any of their children’s children or any information it would be so much appreciated.

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