STRUCTURE OF SOCIAL SECURITY NUMBERS

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".

The process of assigning numbers has been changed at least twice.
Until 1965, only half the group numbers were used. Before 1972,
numbers were assigned by field offices; since 1972, they have all been
assigned by the central office. The order in which numbers were
assigned was changed in the 1972 transition. There may have been other
changes, but it's difficult to get information on how things used to be
done.

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 SSNs
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.

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 627-645 TX
268-302 OH 520 WY 646-647 UT
303-317 IN 521-524 CO 648-649 NM
318-361 IL 525 NM *Guam, American Samoa,
362-386 MI 526-527 AZ Philippine Islands,
387-399 WI 528-529 UT Northern Mariana Islands
650-699 unassigned, for future use
700-728 Railroad workers through 1963, then discontinued
729-799 unassigned, for future use
800-999 not valid SSNs.

Some sources have claimed that numbers
above 900 were used when some state programs were converted to
federal control, but current SSA documents claim no numbers above 799
have ever been used.

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:
Odd numbers, 01 to 09
Even numbers, 10 to 98
Even numbers, 02 to 08
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.

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:
• Any field all zeroes (no field of zeroes is ever assigned).
• First three digits above 740
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.
This description of the structure of the Social Security Number is
based on messages written by Jerry Crow and Barbara Bennett. The
information has been verified by its correspondence to the SSA's
Program Operations Manual System (POMS) Part 01, Chapter 001,
subchapter 01, which can be found at Federal Depository Libraries.
(SSA Pub. No. 68-0100201.)

I hope this helps I will continue to post this and hopefully some of you can use this.

Enjoy,
David Powers