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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.

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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.

The following table might become out of date. The SSA currently maintains an up-to-date version.

  

 with an asterisk* is a change effective 12/01/05.

This list shows the SSN area and group 

numbers that are in the process of being issued as of the date 

at the top of this page.



NOTE: INDICATES GROUP CHANGE SINCE LAST MONTH.

001 04  002 02	003 02	004 06	005 06 	006 06

007 06*	008 88	009 88	010 88  011 88  012 88

013 88	014 88	015 88	016 88	017 88	018 88

019 88	020 88	021 88	022 88	023 88	024 88

025 88	026 88	027 88	028 88	029 88	030 88

031 88	032 88*	033 86	034 86	035 72	036 70

037 70	038 70	039 70	040 08	041 08  042 08

043 08	044 08	045 08	046 08	047 08	048 06

049 06	050 94	051 94	052 94	053 94	054 94

055 94	056 94	057 94	058 94	059 94  060 94 

061 94  062 94  063 94  064 94  065 94	066 94

067 94	068 94	069 94	070 94	071 94	072 94

073 94	074 94	075 94	076 94	077 94	078 94

079 94	080 94	081 94	082 94	083 94	084 94

085 94	086 94	087 94	088 94	089 94	090 94

091 94	092 94	093 94	094 94	095 94	096 94

097 94	098 94	099 94	100 94	101 94	102 94

103 94	104 94	105 94	106 94	107 94	108 94

109 94	110 94	111 94	112 94	113 94  114 94

115 94  116 94  117 94  118 94  119 94	120 94

121 94	122 94	123 94	124 94*	125 94*	126 94*

127 92	128 92	129 92	130 92	131 92	132 92

133 92	134 92	135 17*	136 15	137 15	138 15

139 15	140 15	141 15	142 15  143 15	144 15

145 15	146 15	147 15	148 15	149 15	150 15

151 15	152 15	153 15	154 15  155 15	156 15

157 15	158 15	159 82	160 82	161 82	162 82

163 82	164 82	165 82	166 82	167 82	168 82

169 82	170 82	171 82	172 82	173 82	174 82

175 82	176 82	177 82	178 82	179 82	180 82

181 82	182 82	183 82	184 82	185 82	186 82

187 82	188 82	189 82	190 82	191 82	192 82

193 82	194 82	195 82  196 82	197 82	198 82

199 82*	200 80	201 80	202 80	203 80	204 80

205 80	206 80	207 80	208 80	209 80	210 80

211 80	212 73	213 73	214 73	215 73	216 73

217 73	218 73	219 73*	220 71	221 02	222 02

223 99	224 99  225 99  226 99  227 99	228 99

229 99	230 99	231 99	232 53	233 51	234 51

235 51	236 51	237 99	238 99	239 99	240 99

241 99	242 99	243 99  244 99  245 99	246 99

247 99	248 99	249 99	250 99	251 99	252 99

253 99	254 99	255 99	256 99	257 99	258 99

259 99	260 99	261 99	262 99	263 99	264 99

265 99	266 99	267 99	268 11	269 11	270 11

271 11	272 11	273 11	274 11	275 11	276 11

277 11	278 11	279 11	280 11	281 11	282 11

283 11	284 11	285 11	286 11  287 11	288 11

289 11*	290 08	291 08	292 08	293 08	294 08

295 08	296 08	297 08	298 08	299 08	300 08

301 08	302 08	303 29	304 29	305 29	306 29

307 29	308 29	309 29	310 29	311 29	312 29

313 29	314 29  315 27	316 27	317 27	318 04

319 04	320 04	321 04	322 04	323 04	324 04

325 04	326 04	327 04	328 04	329 04	330 04

331 04	332 04	333 04	334 04  335 04  336 04

337 04	338 04	339 04	340 04	341 04	342 04

343 04	344 04	345 04	346 04	347 04	348 04

349 04	350 04	351 04*	352 04*	353 02	354 02

355 02	356 02	357 02	358 02	359 02	360 02

361 02	362 33*	363 31	364 31	365 31	366 31

367 31	368 31	369 31	370 31	371 31	372 31

373 31	374 31	375 31	376 31	377 31	378 31

379 31	380 31	381 31	382 31	383 31	384 31

385 31	386 31  387 27	388 27	389 27	390 27

391 27*	392 25	393 25  394 25	395 25	396 25

397 25	398 25	399 25	400 65	401 65	402 65* 

403 63	404 63	405 63	406 63	407 63	408 99

409 99	410 99	411 99  412 99	413 99	414 99

415 99	416 59	417 59	418 59	419 59	420 59

421 59*	422 57	423 57	424 57	425 97	426 97

427 97	428 97	429 99	430 99	431 99	432 99

433 99	434 99	435 99	436 99	437 99	438 99

439 99  440 21	441 21	442 21	443 21	444 21

445 19	446 19	447 19	448 19	449 99	450 99

451 99	452 99	453 99	454 99	455 99	456 99

457 99	458 99	459 99	460 99	461 99	462 99

463 99	464 99	465 99	466 99	467 99	468 47

469 47	470 47	471 47	472 47	473 47	474 45

475 45	476 45	477 45	478 35	479 35	480 35

481 35  482 35	483 35	484 35	485 33	486 23

487 23	488 23	489 23	490 23	491 23	492 23

493 23	494 23*	495 21	496 21	497 21	498 21

499 21  500 21	501 31	502 31	503 37  504 37

505 49	506 49	507 49	508 49*	509 25	510 25

511 25	512 25	513 25  514 23	515 23	516 41

517 41	518 73	519 71  520 51* 521 99	522 99

523 99	524 99	525 99	526 99	527 99	528 99

529 99	530 99	531 57	532 57	533 57	534 57

535 57  536 57	537 57	538 57*	539 55	540 69

541 69	542 69	543 69	544 69	545 99	546 99

547 99	548 99	549 99	550 99	551 99	552 99

553 99	554 99	555 99	556 99	557 99	558 99

559 99	560 99	561 99	562 99	563 99	564 99

565 99	566 99	567 99	568 99	569 99	570 99

571 99	572 99	573 99	574 45	575 99	576 99

577 41	578 39  579 39	580 37	581 99	582 99

583 99	584 99	585 99	586 57	587 97	589 99

590 99	591 99	592 99	593 99  594 99  595 99

596 80	597 80*	598 78	599 78	600 99	601 99

602 55*	603 53	604 53	605 53	606 53	607 53

608 53	609 53	610 53	611 53	612 53	613 53

614 53	615 53	616 53	617 53	618 53	619 53

620 53	621 53	622 53*	623 53* 624 53*	625 53*

626 53*	627 98	628 98	629 98	630 98	631 98

632 98	633 98	634 98	635 98	636 98	637 98

638 98	639 98	640 98* 641 98*	642 98*	643 98*

644 96	645 96	646 84  647 84	648 38	649 38

650 38  651 38*	652 36  653 36	654 22	655 22*

656 20	657 20	658 20	659 12  660 12* 661 10  

662 10  663 10  664 10 	665 10	667 28  668 28 

669 28  670 28*	671 26 	672 26	673 26	674 26  

675 26  676 10  677 10* 678 09  679 09	680 72*

681 09	682 09  683 09  684 09	685 09* 686 07

687 07 	688 07 	689 07	690 07	691 03  692 03

693 03  694 03* 695 01  696 01  697 01 	698 01

699 01  700 18	701 18  702 18  703 18  704 18	

705 18  706 18	707 18  708 18  709 18  710 18  

711 18	712 18	713 18  714 18  715 18  716 18  

717 18	718 18	719 18  720 18  721 18  722 18  

723 18	724 28	725 18  726 18  727 10	728 14  

729 07*	730 05 	731 05  732 05	733 05 	750 03 	

751 03 	756 01  757 01  758 01  759 01* 764 58 

765 58*	766 44	767 44	768 44	769 44*	770 44*	

771 44* 772 42	

This list is from the SSA's web site, which shows the highest group number assigned for each area.

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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.

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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.

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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 770

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.)

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