Structure of Social Security Numbers

                 Structure of Social Security Numbers
                      information contributed by
                            Jerry Crow ( and
                            Barbara Bennett

A Social Security Number (SSN) consists of nine digits, commonly written as
three fields separated by hyphens: AAA-GG-SSSS.  The first three-digit field
is called the "area number".  The central, two-digit field is called the
"group number".  The final, four-digit field is called the "serial number".

Area Numbers

The area numbers were assigned to geographical locations in a manner
analogous to the way in which 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).  With few
exceptions, each geographical area is assigned a range of area numbers.
Area numbers assigned prior to 1972 are an indication of the location of the
SSA office which originally issued the SSN.  Since 1972 SSNs have been
issued centrally and the area number in SSNs assigned since 1972 corresponds
to the residence location of the applicant as indicated on the application
for the SSN.

The original range of area number assignments for a particular region, was,
in many cases, eventually exhausted because of population increases.  The
original area number assignments have been augmented as required.  All of
the original assignments were less than 600 (except for the 700-729 railroad
worker series mentioned above).  Only recently have group numbers in the 600
series been allocated.  An area number in the 800 series is bogus, so any
SSN beginning with an "8" is invalid.  An area number of "000" is also

    000     unused   387-399 WI    528-529 UT
    001-003 NH       400-407 KY    530     NV
    004-007 ME       408-415 TN    531-539 WA
    008-009 VT       416-424 AL    540-544 OR
    010-034 MA       425-428 MS    545-573 CA
    035-039 RI       429-432 AR    574     AK
    040-049 CT       433-439 LA    575-576 HI
    050-134 NY       440-448 OK    577-579 DC
    135-158 NJ       449-467 TX    580     VI Virgin Islands
    159-211 PA       468-477 MN    581-584 PR Puerto Rico
    212-220 MD       478-485 IA    585     NM
    221-222 DE       486-500 MO    586     PI Pacific Islands*
    223-231 VA       501-502 ND    587-588 MS
    232-236 WV       503-504 SD    589-595 FL
    237-246 NC       505-508 NE    596-599 PR Puerto Rico
    247-251 SC       509-515 KS    600-601 AZ
    252-260 GA       516-517 MT    602-626 CA
    261-267 FL       518-519 ID    *Guam, American Samoa,
    268-302 OH       520     WY     Northern Mariana Islands,
    303-317 IN       521-524 CO     Philippine Islands
    318-361 IL       525     NM
    362-386 MI       526-527 AZ

  627-699 unassigned, for future use

  700-728 Railroad workers through 1963, then discontinued
  729-899 unassigned, for future use
  900-999 not valid SSNs, but were used for program purposes
            when state aid to the aged, blind and disabled was
            converted to a federal program administered by SSA.

Group Numbers

The group number is not related to geography but rather to the order in
which SSNs are issued for a particular area.  The 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

A group code of "00" is invalid.

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.

Serial Numbers

Serial numbers are assigned in chronological order as the applications are
processed (except that all 2000 and 7000 series serial numbers are special;
see below).  Serial number "0000" is invalid.

Composite SSN Assignment

The composite numbers are assigned starting with serial number 0001 and
running through all assigned area numbers for the first group code.  Then
serial number 0002 is used with all assigned area numbers for the first
group code.  Etc., etc.  Thus, the area numbers vary first (ascending order
within the assigned range of numbers), followed by the serial numbers (in
ascending order, except for 2000 and 7000 series; see below), followed by
the group numbers (according to the rules above).  Since the group number is
non-repeating and assigned according to a fixed (albeit weird) rule set, it
is an indicator of the age of the SSN.

For example, Idaho is assigned area numbers 518-519.  The SSNs in Idaho,
then, were assigned in the following order:

518-01-0001, 519-01-0001, 518-01-0002, 519-01-0002 ..... 518-01-9999,
519-01-9999, 518-03-0001, 519-03-0001, etc.

The 2000 and 7000 series serial numbers are special.  These ranges are not
assigned in chronological order.  Rather, every fifth applicant is assigned
a serial number in one of these ranges.  These serial number groups
represent a random sampling of SS participants and are used for statistical

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 digit "8" (no area numbers in the 800 series have been assigned).
3.  First two digits 73-79 (no area numbers in the 700 series have been
    assigned except for the "railroad" series, 700-729).

Very few SSNs with an area number in the 900 series have been allocated and
virtually all of them are special numbers (i.e., they are not assigned to

A pamphlet entitled "The Social Security Number" (Pub. No.
05-10633) provides an explanation of the SSN's structure and
the method of assigning and validating Social Security numbers.

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