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

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

The 1940 census of the United States is a particularly exciting one for genealogy research for a number of reasons — the most obvious being that is was only indexed and released for public consumption a few years ago. The new records gave many of us a special chance to add vital new details to the our ancestors’ stories.

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.

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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.



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.

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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

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Leave a response
  • Cheryl
    September 12, 2017 at 11:32 am

    It’s kind of cool. I did notice it because my father was one of the two people. He was 7 years old.

  • María del Carmen
    December 18, 2016 at 11:46 am

    Desearía saber de que lugar de Italia eran mis abuelos paternos, Antonio Abate y Antonia Santoiani. Se que mi abuelo era viudo y llegó aproximadamente alrededor del 1890. Se casó en Argentina con mi abuela y tuvo ocho hijos. Toda información, será maravilloso. Muy agradecida. Atte. María del Carmen Abate

  • Ana Maria Pesle
    November 8, 2016 at 7:44 pm

    Busco mis antepasados maternos: Costantini- Sbardelatti (italia) paterno: Pesle-Suarez

  • Amalia Beatriz Jayo
    August 27, 2016 at 8:33 am

    ¿En español?

  • D. K. LeMay
    August 6, 2016 at 12:16 pm

    Whomever interviewed my aunt Louise Guaragna, residence Massachusetts (married abt 10 years with 3 daughters) MIXED UP her responses with the other person on the page–a 17 year old single girl!!

    Hoping this can be corrected!

    • Laurie
      June 10, 2017 at 4:43 pm

      Depending on where you view the page, there might be a comment / correction section. Ancestry has that, I haven’t seen it elsewhere. I’d chose comment, then add this explanation so others will see it and know too.

    • Beverly Niebruegge
      November 28, 2017 at 5:27 pm

      How can we correct this info. My dad had a similar problem?

  • Caroline Brown
    August 4, 2016 at 8:27 pm

    When trying to read the 1940s census for my parents, I could not make out the columns so I downloaded a PDF “How to Read the 1940s Census.” It was the instructions to the census takers. In the column for address, it states list the house numbers in numerical order. That was for column three. But on my parents page the letter “T” appears for all the names. Further instructions: use the letter “T” for those individuals in a camp, hotel, trailer park, etc. My parents were in Benson, Arizona in April 1940. I never heard them mention Arizona but I determine from what I do know of that year of their life they were on their way to San Diego, where I was born, from Missouri, where they met and married, for a job my dad had secured in the aircraft industry.

  • Ann Rossi
    January 31, 2016 at 7:53 am

    Be a diligent researcher. In 1940 my mother age 17 is listed 4 times. My fathers family in Hickman county Swan Creek is lusted twice!

  • Mark
    January 18, 2016 at 9:45 am

    Don’t forget the circle with an “x” in it next to a name. That indicates the person who provided the information. So, unlike previous census’, you can tell WHO provided the information. That can help you judge the reliability of the info.

  • James Guth
    October 18, 2015 at 2:31 pm

    Another important entry in the 1940 census is an individual’s place of residence on 1 April 1935. This is especially helpful in tracing newlyweds back to where they may have met and married. Children under the age of five should not have a location in this section, but occasionally an enumerator did fill in the blanks for the entire family whether they applied or not. Careless is not a new thing.

  • Walt Westcott
    October 14, 2015 at 7:44 pm

    How does it happen that a census taker in 1940 would end a dead end street with at least two homes left to survey ? They were and are visible from the last he surveyed.

    • L. Kilzer
      July 29, 2016 at 2:01 pm

      I’m no expert, but am wondering if maybe the people were not at home and the census taker didn’t bother to go back later. I haven’t been able to find my step-grandfather and his family in the 1940 census, and a friend of mine suggested that maybe they were not at home.

    • Bonnie Temleton
      August 1, 2016 at 7:33 pm

      Maybe them weren’t built until after 1940.

  • Allegheny county PA, Port vue, Elizabeth twsp, Legionier, Clairton, McKeesport
    September 19, 2015 at 3:39 pm

    Kelley, Graham, O’Nise, Coughenhour, McCaffery, 1880- 1970

  • Bettejean Spatafore
    September 5, 2015 at 5:40 am

    What would “af” after a persons name stand for? The person in question was 18 years old and a first year college student. Does this mean he was away at school? Thank you.

  • Betty Jo Woodside Kelley
    September 4, 2015 at 6:22 am

    Always looking for ancestors.

Leave a Response