Deciphering the SSN

SSN thumbIn a recent post about’s U.S., Social Security Applications and Claims Index, 1936-2007 database it was mentioned that the gentleman in the example had previously had an account starting with a 700 number. This was significant as the low 700 numbered accounts were reserved for the Railroad Retirement Board.  This indicated this person had worked for a railroad, something we may not have known before.  Are there other secrets held within the Social Security Number (SSN) sequences?

What is the SSN Numbering Scheme?

 The nine-digit SSN is composed of three parts:

  • The first set of three digits is called the Area Number
  • The second set of two digits is called the Group Number
  • The final set of four digits is the Serial Number

Area Number

The Area Number was assigned by the geographical region.  Prior to 1972, cards were issued in local Social Security offices around the country and the Area Number represented the State in which the card was issued.  This did not necessarily have to be the State where the applicant lived, since a person could apply for their card in any Social Security office.  Since 1972, when SSA began assigning SSNs and issuing cards centrally from Baltimore, the area number assigned has been based on the ZIP code in the mailing address provided on the application for the original Social Security card.  The applicant’s mailing address does not have to be the same as their place of residence.  Thus, the Area Number does not necessarily represent the State of residence of the applicant, either prior to 1972 or since.

Generally, numbers were assigned beginning in the northeast and moving westward.  So people on the east coast have the lowest numbers and those on the west coast have the highest numbers.  It was not meant to supply useable geographical information.  The numbering scheme was designed in 1936, before computers, to make it easier for SSA to store the applications in their files in Baltimore.  The files were organized by regions, as well as alphabetically.  It was really just a bookkeeping device used by the SSA in the days of paper files and metal file cabinets.

 Group Number

Within each area, the group number (middle two (2) digits) range from 01 to 99 but are not assigned in consecutive order. For administrative reasons, group numbers issued first consist of the ODD numbers from 01 through 09 and then EVEN numbers from 10 through 98, within each area number allocated to a State.  After all numbers in group 98 of a particular area have been issued, the EVEN Groups 02 through 08 are used, followed by ODD Groups 11 through 99.

SSN Group

Serial Number

Within each group, the serial numbers (last four (4) digits) run consecutively from 0001 through 9999.

What can the Genealogist Discern from a SSN?

As was mentioned in the introduction, numbers starting with 700-728 were previously assigned to the Railroad Retirement Board.  While they have no geographic information, we do know that the SSN holder worked in the railroad industry at one point in time.  The issuance of these numbers to railroad employees was discontinued 1 July 1963.

Prior to 1972 SSNs were issued by regional field offices.  This function was centralized in Baltimore in 1973 where the numbers were assigned based on the first 3 digits of the applicants mailing address. This distribution is shown in the table below.

SSN Table

While these Area Numbers were not meant to imply place of birth, or normal residence, it does give us an indication where our ancestor was when he or she applied for a SSN.  This is particularly useful during the Great Depression years, when people sometimes moved great distances for employment.  The Census Bureau was probing this same issue when they asked for place of residence on 1 April 1935 in the 1940 census.  I have found this to be a useful strategy in locating family members that seem to disappear in the 1930’s and 40’s.

It is also helpful when you are looking at the Social Security Death index.  Imagine the scenario where you are looking for great uncle John Joseph Smith.  You lost track of Uncle Jack in 1920 where he was listed in the census as a farm hand on his father’s farm in Iowa.  You are given a choice of 2 men in the SSDI: one man applied for a SSN in Maine, the other in Nebraska.  While it is possible that Jack hated farming and went off to Maine to be a lobsterman, our time would probably be best spent researching the man in Nebraska first.

In March, 2015 the 729-733 numbers were designated Enumeration at Entry (EAE).  SSA has agreements with the Department of Homeland Security (DHS) and the Department of State (DoS) to assist SSA in enumerating immigrants admitted as lawful permanent residents. If an immigrant wishes to apply for an original SSN under the EAE process, DoS collects enumeration data during the immigrant visa process, and electronically transmits the data to DHS. When the immigrant is admitted into the U.S., DHS electronically transmits the enumeration data to SSA so that an SSN can be assigned.

Stephen P. Morse offers a One-Step tool, “Decoding Social Security Numbers,” in which you can determine the year and state of application for any SSN issued prior to 2011.  Why does this tool stop at 2011?  On 25 June 2011 the Social Security Administration changed the way SSNs are issued.  This change is referred to as “randomization. “The SSA developed this new method to help protect the integrity of the SSN.  SSN Randomization will also extend the longevity of the nine-digit SSN nationwide.

SSN randomization affected the SSN assignment process in the following ways:

  • It eliminated the geographical significance of the first three digits of the SSN, referred to as the area number, by no longer allocating the area numbers for assignment to individuals in specific states.
  • It eliminated the significance of the highest group number and, as a result, the High Group List is frozen in time and can only be used to see the area and group numbers SSA issued prior to the randomization implementation date.
  • Previously unassigned area numbers were introduced for assignment excluding area numbers 000, 666 and 900-999.


While the Area Number was never intended to provide information about the residence of an applicant, and the Group Number was only meant to indicate a group of Serial Numbers (not any particular group of people), together they can point the researcher to a state and timeframe that an ancestor applied for a SSN.  This may be the clue you have needed to connect two seemingly unrelated individuals.

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One Response to Deciphering the SSN

  1. Barbara says:

    A very useful article. Thanks!

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