Structure of Social Security Numbers
by Chris Hibbert
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
429-432
AR
585
NM
004-007
ME
433-439
LA
586
Guam
008-009
VT
440-448
OK
586
American Samoa
010-034
MA
449-467
TX
586
Pacific Islands*
035-039
RI
468-477
MN
587-588
MS
040-049
CT
478-485
IA
589-595
FL
050-134
NY
486-500
MO
596-599
Puerto Rico
135-158
NJ
501-502
ND
600-601
AZ
159-211
PA
503-504
SD
602-626
CA
212-220
MD
505-508
NE
627-645
TX
221-222
DE
509-515
KS
646-647
UT
223-231
VA
516-517
MT
648-649
NM
232
NC
518-519
ID
650-653
CO
232-236
WV
520
WY
654-658
SC
237-246
NC
521-524
CO
659-665
LA
247-251
SC
525
NM
667-675
GA
252-260
GA
526-527
AZ
676-679
AR
261-267
FL
528-529
UT
680
NV
268-302
OH
530
NV
681-690
NC
303-317
IN
531-539
WA
691-699*
VA
318-361
IL
540-544
OR
729-733
Enumeration at Entry
362-386
MI
545-573
CA
750-751*
HI
387-399
WI
574
AK
752-755*
MI
400-407
KY
575-576
HI
756-763*
TN
408-415
TN
577-579
DC
764-765
AZ
416-424
AL
580
Virgin Islands
766-772
FL
425-428
MS
580-584
Puerto Rico
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:
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" are not 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:
1. Any field all zeroes (no field of zeroes is ever assigned).
2. First three digits above 740
000-XX-XXXX
XXX-00-XXXX
XXX-XX-0000
740-XX-XXXX
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.)
If the person you are searching for is dead you may want to try this to see what information they
have on file.
