Here's the info we have on SS Numbers. The source is in a pamphlet entitled
"The Social Security Number" (Pub. No. 05-10633). It provides an explanation
of the SSNs structure and the method of assigning and validating Social
Security numbers. Information about SSN assignment can be found in the SSA's Program Operations
Manual System (POMS) Part 01, Chapter 001, subchapter 01, which is located at
Federal Depository Libraries. (SSA Pub. No. 68-0100201.).

Area Numbers
The area numbers are assigned to geographical locations. They were originally
assigned the same way that zip codes were later assigned (in particular, area
numbers increase from east to west across the continental US as do the ZIP
codes). Most area numbers were assigned according to state (or territorial)
boundaries, although the series 700-729 was assigned to railroad workers
regardless of location (this series of area numbers was discontinued in 1964
and is no longer used for new SSNs). Area numbers assigned prior to 1972 are an
indication of the SSA office which originally issued the SSN. Since 1972 the
area number in the SSN corresponds to the residence address given by the
applicant on the application for the SSN.

In many regions the original range of area number assignments was eventually
exhausted as population grew. The original area number assignments have been
augmented as required. All of the original assignments were less than 585
(except for the 700-729 railroad worker series mentioned above). Area numbers
of "000" have never been issued.

Group Numbers
The group number is not related to geography but rather to the order in which
SSNs are issued for a particular area. Before 1965, only half the group
numbers were used: odd numbers were used below 10 and even numbers were used
above 9. In 1965 the system was changed so assignments continued with the low
even numbers and the high odd numbers. So, group numbers for each area number
are assigned in the following order:

  • 1. Odd numbers, 01 to 09
  • 2. Even numbers, 10 to 98
  • 3. Even numbers, 02 to 08
  • 4. Odd numbers, 11 to 99

  • Group codes of "00" aren't assigned

    In each region, all possible area numbers are assigned with each group number
    before using the next group number. This means the group numbers can be used
    to find a chronological ordering of SSNs within a region. When new group
    numbers are assigned to a state, the old numbers are
    usually used up first. SSA publishes a list every month of the highest group
    assigned for each SSN Area. For example, if the highest group assigned for
    area 999 is 72, then we know that the number 999-04-1234 is an
    invalid number because even Groups under 9 have not yet been assigned.

    So the group numbers have nothing to do with a person's DOB. but do give an
    indication of the YEAR the SS# was issued in. It has only been about 10 years or so that
    Social Security began issuing it's numbers at birth. For most of your missing persons
    and skips however, SS#'s were frrst acquired and required for employment
    purposes. If you know the SS#, but do not know the DOB, you can approximate how old your
    subject is by looking at the middle 2 numbers and decoding them. These numbers
    for most of us, were issued on or about age 16.
    To validate a SS#, see what state it was issued in, and year range right online NOW,
    click on the following link:


    Serial Numbers
    Serial numbers are assigned in chronological order within each area and group
    number as the applications are processed. Serial number "0000" is never used.
    Before 1965, when number assignment was transferred from field offices to the
    central office, serial numbers may have been assigned in a strange order.
    (Some sources claim that 2000 and 7000 series numbers were assigned out of
    order. That no longer seems to be the case.) Currently, the serial numbers are
    assigned in strictly increasing order with each area and group combination.

    Invalid SSNs
    Any SSN conforming to one of the following criteria is an invalid number:

    1. Any field all zeroes (no field of zeroes is ever assigned).
    2. First three digits above 740


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