The Format of the Social Security numbers was historically broken into 3 parts.
Area
3 Digits, The Area was assigned to States, US territories, or special use areas such as 'enumeration at entry' or for a brief period of the time Rail Road use employees (ended July 1, 1963). Of note is that this is from the STATE or area that person Applies, not necessarily where they are born. From 1973 - July 14, 2011 the Area was assigned by looking at the zip code shown on the mailing address that was used for the application. Before 1973 the The number was assigned by a field office. Area number of 000 is never assigned. For religious reasons, 666 was never allocated for assigment by SSA. As of 2009, area 772 was considered the highest issued area number and at the time was used to help identify fraudulent numbers.
Group
2 Digits, These were assigned in a sequency and it is from this number that approximate age of a SSN can be determined. This is the order a number was assigned in a particular AREA, and do not have any geographic designation. Historically SSA published a list of of the last used GROUP number by region and this is how age of the group was determined. This report was called "Highest Group Issued" or highgroup.txt (see below) and until SSN assignment was moved to Random, this report was key to determining fraudulent numbers. If a number was not yet used by a region it was fraudulent. If someone claims a SSN that was allocated before the person was born, then it is most probably fraudulent. Group 00 is never used.
Order of issuance was:
Odd 01-09
Even 10-98
Even 02-08
Odd 11-99
Block
5 Digits, NumChk reports on approximately 100,000 of these numbers or blocks and this is how the content is organized.
Serial
4 Digits, this is the serial number portion of a SSN number. Because the first 5 digits of older SSN numbers can be determined by State/Region and approximate date of issue, the Serial number is the only real 'secret' part of the number. Unfortunately, many publish this part of the number to confirm the number is yours, and this is the hardest part of the number to determine in most cases if someone were to brute force attack (try to guess) your SSN, so by people publishing this they are doing you a disservice - and further exposing you to identify theft. Even if left to brute force, at only 4 digits, this leaves 10k combinations that is still trivial to determine. Serial 0000 is never assigned.
Serial numbers are normally assigned in chronological order within each area and group number as the applications are processed. Before 1965, serial numbers may have been assigned in a strange order. Reports are 2000 and 7000 series numbers were assigned out of order. From 1965 - 2011 the serial numbers were assigned in strictly increasing order with each area and group combination.
Since 2011 and Randomization - all new numbers including the Serial number are random from valid number allocations and no longer to determine the order, and thus approximate age of issuance.
An Example of the highgroup.txt file historically published by the SSA.
HIGHEST GROUP ISSUED AS OF 7/01/08
Anything with an asterisk (*) is a change effective 7/01/08.
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 06 002 06 003 06 004 08 005 08 006 08
007 08 008 92 009 90 010 92 011 92 012 92*
013 90 014 90 015 90 016 90 017 90 018 90
019 90 020 90 021 90 022 90 023 90 024 90
025 90 026 90 027 90 028 90 029 90 030 90
031 90 032 90 033 90 034 90 035 72 036 72
037 72 038 72 039 72 040 13 041 13 042 13
043 11 044 11 045 11 046 11 047 11 048 11
049 11 050 98 051 98 052 98 053 98 054 98
055 98 056 98 057 98 058 98 059 98* 060 98*
061 98* 062 98* 063 96 064 96 065 96 066 96
067 96 068 96 069 96 070 96 071 96 072 96
073 96 074 96 075 96 076 96 077 96 078 96
079 96 080 96 081 96 082 96 083 96 084 96
085 96 086 96 087 96 088 96 089 96 090 96
091 96 092 96 093 96 094 96 095 96 096 96
097 96 098 96 099 96 100 96 101 96 102 96
103 96 104 96 105 96 106 96 107 96 108 96
109 96 110 96 111 96 112 96 113 96 114 96
115 96 116 96 117 96 118 96 119 96 120 96
121 96 122 96 123 96 124 96 125 96 126 96
127 96 128 96 129 96 130 96 131 96 132 96
133 96 134 96 135 19 136 19 137 19 138 19
139 19 140 19 141 19 142 19 143 19 144 19
145 19 146 19 147 19 148 19 149 19 150 19
151 19 152 19 153 19 154 19 155 19 156 19
157 19 158 19* 159 84 160 84 161 84 162 84
163 84 164 84 165 84 166 84 167 84 168 84
169 84 170 84 171 84 172 84 173 84 174 84
175 84 176 84 177 84 178 84 179 84 180 84
181 84 182 84 183 84 184 84 185 84 186 84
187 84 188 84 189 84 190 84 191 84 192 84
193 84 194 84* 195 84* 196 82 197 82 198 82
199 82 200 82 201 82 202 82 203 82 204 82
205 82 206 82 207 82 208 82 209 82 210 82
211 82 212 81 213 81 214 81 215 81 216 81
217 81 218 81 219 81* 220 79 221 06 222 06
223 99 224 99 225 99 226 99 227 99 228 99
229 99 230 99 231 99 232 55 233 55 234 53
235 53 236 53 237 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 13 269 13 270 13
271 13 272 13 273 13 274 13 275 13 276 13
277 13 278 13 279 13 280 13 281 13 282 13
283 13 284 13 285 13 286 13 287 13 288 13
289 13 290 13 291 13 292 13 293 13 294 13
295 13 296 13 297 13 298 13 299 13* 300 13*
301 11 302 11 303 33 304 33 305 33 306 33
307 33 308 33 309 33 310 33 311 33 312 31
313 31 314 31 315 31 316 31 317 31 318 08
319 08 320 08 321 08 322 08 323 08* 324 08*
325 06 326 06 327 06 328 06 329 06 330 06
331 06 332 06 333 06 334 06 335 06 336 06
337 06 338 06 339 06 340 06 341 06 342 06
343 06 344 06 345 06 346 06 347 06 348 06
349 06 350 06 351 06 352 06 353 06 354 06
355 06 356 06 357 06 358 06 359 06 360 06
361 06 362 35 363 35 364 35 365 35 366 35
367 35 368 35 369 35 370 35 371 35 372 35
373 35 374 35 375 35* 376 35* 377 33 378 33
379 33 380 33 381 33 382 33 383 33 384 33
385 33 386 33 387 29 388 29 389 29 390 29
391 29 392 29 393 29 394 29 395 29 396 29
397 29 398 29 399 29 400 69 401 69 402 69
403 69 404 67 405 67 406 67 407 67 408 99
409 99 410 99 411 99 412 99 413 99 414 99
415 99 416 63 417 63 418 63 419 63 420 63
421 63 422 61 423 61 424 61 425 99 426 99
427 99 428 99 429 99 430 99 431 99 432 99
433 99 434 99 435 99 436 99 437 99 438 99
439 99 440 25 441 25 442 25* 443 23 444 23
445 23 446 23 447 23 448 23 449 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 51
469 51 470 51 471 51 472 51 473 51 474 51
475 51 476 51 477 51* 478 39 479 39 480 39
481 37 482 37 483 37 484 37 485 37 486 27
487 27 488 27* 489 25 490 25 491 25 492 25
493 25 494 25 495 25 496 25 497 25 498 25
499 25 500 25 501 33 502 33 503 41 504 41
505 53 506 53 507 53 508 53* 509 29 510 29
511 29 512 29* 513 27 514 27 515 27 516 45
517 45 518 81* 519 79 520 55 521 99 522 99
523 99 524 99 525 99 526 99 527 99 528 99
529 99 530 99 531 65* 532 63 533 63 534 63
535 63 536 63 537 63 538 63 539 63 540 75
541 75 542 75 543 75 544 75 545 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 53* 575 99 576 99
577 47 578 47* 579 45 580 39 581 99 582 99
583 99 584 99 585 99 586 63* 587 99 588 03
589 99 590 99 591 99 592 99 593 99 594 99
595 99 596 86 597 86 598 86* 599 84 600 99
601 99 602 71* 603 71* 604 71* 605 71* 606 71*
607 71* 608 69 609 69 610 69 611 69 612 69
613 69 614 69 615 69 616 69 617 69 618 69
619 69 620 69 621 69 622 69 623 69 624 69
625 69 626 69* 627 15 628 15 629 15 630 15
631 15 632 15 633 15 634 15 635 15 636 15
637 15 638 15* 639 15* 640 15* 641 15* 642 13
643 13 644 13 645 13 646 04* 647 02 648 48
649 46 650 50 651 50* 652 48 653 48 654 30*
655 28 656 28 657 28 658 28 659 18* 660 16
661 16 662 16 663 16 664 16 665 16 667 38
668 38 669 38* 670 38* 671 38* 672 36 673 36
674 36 675 36 676 16 677 16* 678 14 679 14
680 98 681 16 682 16 683 16 684 16* 685 16*
686 14 687 14 688 14 689 14 690 14 691 10*
692 10* 693 09 694 09 695 09 696 09 697 09
698 09 699 09 700 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 14 730 14 731 12 732 12 733 12
750 10 751 10 752 03 753 03 754 01 755 01
756 07 757 07 758 07 759 07 760 05 761 05
762 05 763 05 764 92* 765 90 766 72 767 72
768 72 769 72* 770 72* 771 72* 772 70
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