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

Last Updated November 24, 2023

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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?

Census.gov 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

NamePerson’s father’s birthplacePerson’s mother’s birthplacePerson’s mother or native tongue

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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

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 marriageNumber 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