Converting Between 1920 and 1930 Census EDs in One Step
Converting Between 1930 and 1940 Census EDs in One Step

Frequently Asked Questions

Stephen P. Morse , San Francisco

1. What is an ED?

ED stands for Enumeration District.  An enumeration district is defined by the National Archives and Records Administration (NARA) as a "basic geographic area of a size that could be covered by a single census taker (enumerator) within one census period."

2. Why do I need to know about EDs?

Starting with the 1880 census, all the information is arranged by ED in the actual census microfilms.  Therefore in order to locate a person, you need to know the ED in which that person resided in that census year.  Determining the ED may or may not be difficult, depending on where the person lived.

There are some name indexes that may be helpful in locating a person in the 1920 census.  But even with such an index, you might not be able to find the person because the name on the census sheet might be illegible and could not be read when the name index was created.  Even if it could be read, it might have been badly misspelled when it was originally entered onto the census sheet or when it was later transcribed into the name index.  In those cases, you'll definitely need the ED number before you can go any further.

3. Why is a conversion between EDs from two different census years so important?

There currently is no online system for finding the 1920 ED of an address.  But there is for finding the 1930 ED for over 400 cities, namely the One-Step 1930 Census ED Finder.  So one way of finding a person in the 1920 census is to obtain the 1930 ED for the person's 1920 address and then use this conversion website to determine the corresponding 1920 ED. Similarly you can use this conversion website for determining the 1940 ED, but that's less significant since the there is a One-Step 1940 Census ED Finder.

Of course this assumes that the street names and house numbers did not change between 1920 and 1930 or between 1930 and 1940.  Two cities that underwent major street name changes around this time period are Baltimore Maryland and Queens New York.  See question 308 on the ED Finder FAQ page for more details on street-name changes.

4. Why are there sometimes more than one 1920 or 1940 ED given for a 1930 ED, and vice versa?

The district boundaries were not the same in the different census periods.  In some cases several 1920 or 1940 EDs might be contained in a single 1930 ED, while in other cases a 1920 or 1940 ED might be split over two or more 1930 EDs.

If you get more than one 1920 or 1940 ED, you might want to narrow things down further before you start looking through all the EDs.  You can do this by looking at a description of the various EDs along with a map of the area.  ED descriptions for various years can be found on NARA microfilm series T1224 (see question 5).

You can obtain the 1920 descriptions online by going to

and then select the desired state, county, and city in sequence.  You will eventually get to a description of the EDs within that city.  This is a free service on so you do not have to be a subscriber to use it.  Such online descriptions for 1940 do not yet exist; when they do we will post the link.

As for a map of the area, you can use or, and hope that the area has not changed.

If you have to look through multiple EDs to find your address, here are some strategies you might want to consider.  The left column of the census form contains the street name written vertically, and the next column contains the street addresses.  So instead of looking for the family name on the census sheet, start by looking for the desired street name and then the desired house number.  Enumerators were instructed to go around a block rather than along several blocks sequentially, so your street name may appear at different places within the census sheets for a particular ED.  See if the house numbers are all even or all odd and compare that to whether you are looking for an even or odd address.  Check the end of the ED sheets where the enumerator may have gone back to find people they missed on the first sweep of the area.

5. Where did this data come from?

NARA has a microfilm series T1224 which give definitions of the ED boundaries for various census years.  For 1930 and 1940 it also includes the corresponding EDs for the previous census.  The data presented here comes from these microfilms, and its accuracy is limited by the accuracy of the information on the microfilms.

For some table entries, we may show NO INFO when you ask for a conversion number.  There are many reasons for this designation, including (but not limited to): missing information on the T1224 films; illegible microfilms; new EDs in areas where there was no coverage on the previous census (such as Civilian Conservation Corps Camps (see question 13) in 1940); or 1930 EDs from areas annexed into the city after the 1920 census enumeration.  We may also use a question mark if there is some possible problems with the conversion number.

After we generated our data from the 1930 T1224 microfilms, we reduced the number of NO INFO and question mark entries by overlaying 1920 and 1930 ED maps and correlating the district boundary definitions.  If there was any uncertainty when we did this correlation, we indicated that with a question mark as well.

The transcribing of the 1920-1930 data was done by a team of volunteers to whom we are very grateful.  That team was headed by Joel Weintraub.  The transcribing of the 1930-1940 data was done entirely by Joel Weintraub; over 149,000 ED conversions were transcribed to provide the tables of our 1930 to 1940 utility.

We cannot vouch for the validity of the T1224 data, nor can we be certain that it has been transcribed accurately.  Of course we hope that it has few errors and that this website is a useful tool for researchers.

6. The list of EDs that I obtain is too long to fit in the field.  How can I see the ones that got truncated?

So you selected Los Angeles for example, and then picked NO INFO from the choices for the 1920 ED.  The resulting list of 1930 EDs is too long to fit in the field.  But it hasn't been truncated.  It's there and you just need to scroll the field.  Place your cursor into the field and then repeatedly press the right-arrow key to move the cursor to the right end of the field.  Once you reach the end, the field will start scrolling.  To scroll back, repeatedly press the left-arrow key until it gets to the left end.

This question doesn't apply in the 1930 to 1940 conversion case.

7. Are there any websites that show which streets were in which 1920 ED?

Not for the entire country.  But for a few select areas there are websites that show this information.  Here are some that we know about.  If you know of any others, please e-mail me and I'll add the links here.

Lowell Area, MA:
Brooklyn, NY:
Cook County, IL:

8. Why is my city, which is large, not shown on your 1920-1930 list?

Nearly all cities (over 400 of them) that are on the One-Step 1930 Census Website are represented on this 1930/1920 utility as well.  The exceptions are a few cities that had no 1920 ED conversions as shown on NARA's T1224 for 1930.  For some of the cities, the T1224 rolls just showed a range of 1920 EDs for a given 1930 ED, and we included that information here.

We then added another 500 + cities from the 1930 T1224 descriptions using the following criteria: the entity had to be a city, not a Precinct or other smaller political unit; the City had to be large enough (usually 4 or more EDs); the T1224 descriptions had to be legible (not light or cut off); and there had to be a direct 1930 to 1920 ED relationship shown (and not a range of 1920 EDs at the start of the city).  Because of these rules, a number of cities with more than 3 EDs were excluded from this database. Such exclusions were not randomly distributed among the states; some states suffered more from the application of our rules than others.

This question doesn't apply to the 1930-1940 converter because that converter covers every ED in the country rather than only in select cities.  So in that case you select the ED directly and not the city.  If the ED is in a city that had at least 5,000 people (about 3 or 4 EDs) in 1940, the city name will likely be displayed when the ED is selected.  Or you can select the city and see what 1940 EDs cover that area.  Our tables cover over 3,000 cities, which include most of the urban areas that contained at least 3 EDs in 1940.

9. What should I do if my city appears on your 1930/1920 list, but doesn't appear on the 1930 ED utility?

Our 1930 ED utility has all cities over 25,000 in the U.S. in 1930, and many smaller ones. It is a street-based system.   If your city is not on that list, use the One-Step 1930 ED Definition tool to find out what your target ED was for 1930 for your address, and then enter that ED into the appropriate One-Step converter to obtain the 1920 or 1940 ED number.

10.  I don't know the address of the person I want.  What do I do?

You need to know where the person lived when the census was taken.  If the person lived in a city or urban area, a street address will be most helpful for finding the ED, although sometimes just the general location will suffice (see last paragraph).  For more rural areas, you'll need county and the name of the town or township.

One source of street addresses are city directories and, starting with the 1940 census, telephone directories.  Private companies compiled the city directories and tried to include every male of employable age, workers under the age of twenty, male students, working women, widows, and girls of marriageable age.  Old city directories and telephone books are generally available in the reference sections of public libraries in large cities and most library reference departments will check a name for free or at a nominal cost; often the request can be made on line or by telephone.

The city directories are also available through the Family History Library.  A useful list of available city directories can be found at the following sites:
FHL City Directories
Other potential sources for a person's location are: Social Security applications, old letters and envelopes, telephone directories, death certificates, birth certificates, naturalization papers, ship manifests, wedding certificates, school records, religious records, voter registration, and U.S. Census records.

If you know the general location that the person lived, it may be possible to find the ED(s) that potentially enclose the site by looking at a city or county ED map.  Such maps are available at the National Archives and are found in microfilm series A3378, "Enumeration District Maps for the Twelfth through Sixteenth Censuses of the United States 1900-1940."  There are 73 rolls in this series and both county and city maps are represented.  The original maps had the EDs drawn with color boundaries and colored numbers, but the film shows them as shades of gray.

11. What is on the 1940 Census sheets and how was that census carried out?

The columns expected on the 1940 Census sheets can be found at the following websites (for the purpose of printing the forms, it's useful to know that the dimensions are 23.75" wide by 18.5" high):
The procedural history of the 1940 Census can be found at:
The 1940 enumerator instructions and some supplementary instructions (Form P-15) can be found at:
Some of the forms used by an enumerator to check on hotel tenant returns (P-8), and a form in the case where a person refused to give his/her wage statement directly to the enumerator (P-16), and the daily report postcard the enumerator was to mail to his/her supervisor (F-100) can be found at:
The new 1940 questions were opposed by many, and a boycott of the census was threatened.  To counter this, the Census Bureau aired some radio broadcasts called "Uncle Sam Calling."  More details on this, as well as transcripts of two of these broadcasts, can be found here.

Joel Weintraub has a growing library of memorabilia on the 1940 enumeration.  If you have additional 1940 items such as census forms or posters, or additional episodes of "Uncle Sam Calling"  that you can add to this collection, and that we might post on this FAQ,  please contact Joel directly.

12. Where can I find out more information on the census and the national results?

Information on summary statistics can be found at the following site:
Specific government reports from the 1940 Census in PDF and zip files can be found at:

13. What are the CCC Camps that you show on the 1940 utility?

During the Great Depression the Civilian Conservation Corps (CCC) was started to  provide gainful employment for millions of Americans and a way to increase  habitat rehabilitation throughout the United States.  The 1940 Census gave separate ED numbers, within their County prefixes,  to the CCC camps.  It appears that the camps were distributed throughout the United States and may have had in excess of 300,000 individuals.  These CCC EDs are unique to the 1940 Census, and apparently have no corresponding 1930 ED numbers.  To make this conversion utility work, we had to assign them an arbitrary ED number in 1930.  So we chose 0-0.  (In some cases the 1940 CCC EDs did show a corresponding 1930 ED number, but we ignored that information in our transcriptions since it had no meaning.)

In transcribing CCC camp locations, we found a number that showed no population on the definitions film.  The camp could have been closed, but in that case the ED could have been shown as "Void".  A possible explanation for this is in the 1940 Enumerator's Handbook where paragraph 327 states that CCC enrollees be counted "at their usual place of residence, and not at the camp in which enrolled, unless they have no other usual place of residence" while employees other than enrollees in a CCC camp would be counted if they slept at the camp.  Thus it's possible that enrollees could be double counted on the 1940 census, or not counted at all because of this determination by the enumerator.

Over 1300 CCC camps are contained in our tables.  But the actual name of the camp was not transcribed for any of them, just the generic name of CCC.

See the following for further information about this very popular program.

14. Why do some 1940 EDs have letters at the end?

If a 1940 Enumeration District involved more work than a single enumerator could handle, that district was subdivided and assigned to several enumerators.  When that happened, letter suffixes were appended to the end of the ED.  An example is 16-167A, 16-167B, and 16-167C.

Over 4,500 (out of a total of 150,000) EDs in 1940 were subdivided.

15a. Why do 1930 and 1940 EDs consist of two numbers separated by a hyphen?
15b.  Why does the number before the hyphen change between the 1930 and 1940 censuses for some locations?

In 1930, the Census Bureau decided to assign two-part numbers to each ED. The first part of the number (prefix) denoted the county within the state, and the second number (suffix) denoted the census district within the county.  The ED prefixes were usually assigned sequentially to the counties in alphabetical order, so a county like Adams might be given a prefix of 1.  Similarly the ED suffixes were usually assigned in alphabetical order by city name.  To make things confusing, does not show the full 1930 ED number, but just the suffix.

In 1940, the Bureau extended the 1930 prefix numbers by assigning unique prefix numbers to the largest cities within the United States.  Such city prefix numbers come after the highest county prefix number within each state.  For example, the Hollywood Knickerbocker Hotel is in the city of Los Angeles, and that city is within the county of Los Angeles.  In 1930, Los Angeles county was assigned prefix 19, and the Knickerbocker Hotel was assigned ED 19-64.  In 1940, Los Angeles county again had prefix 19, but Los Angeles city was split out and given its own prefix of 60.  So in 1940 the Knickerbocker Hotel was assigned ED 60-132.  To be sure there are actually two other ED 132s in Los Angeles county in 1940 -- namely ED 19-132 which covers part of the city of  Downey and ED 59-132 in the large city of  Long Beach (with its own, new prefix).

-- Steve Morse