A social security number consists of nine digits separated by a hyphen. The first three digit field is called the area number. The middle two numbers is called the group number and the final four numbers are called the serial number.

The area numbers (the first three digits of a social security number) are assigned to geographical locations. They were originally assigned the same way that zip codes were later assigned. The area numbers increase from east to west across the United States like zip codes do. The area numbers are assigned according to state boundries with the exception of railroad workers whose area numbers are 700-729 regardless of location. The railroad workers series of numbers was discontinued and is no longer used for new social security numbers.

If the social security number was issued prior to 1972 the area number indicated the social security office that originally issued the social security number. After 1972 the social security number corresponds to the residence address given on the application for the social security number.

Below is a break down of the area numbers and the states assigned to each series.

001-003 NH
004-007 ME
008-009 VT
010-034 MA
035-039 RI
040-049 CT
050-134 NY
135-158 NJ
159-211 PA
212—220 MD
221-222 DE
223-231 VA
232 NC
232-236 WV
237-246 NC
247-251 SC
252-260 GA
261-267 FL
268-302 OH
303-317 IN
318-361 IL
363-386 MI
387-399 WI
400-407 KY
408-415 TN
416-424 AL
425-428 MS
429-432 AR
433-439 LA
440-448 OK
449-467 TX
468-477 MN
478-485 IA
486-500 MO
501-502 ND
503-504 SD
505-508 NE
509-515 KS
516-517 MT
518-519 ID
520 WY
521-524 CO
525 NM
526-527 AZ
528-529 UT
530 NV
531-539 WA
540-544 OR
545-573 CA
574 AK
575-576 HI
577-579 DC
580 Virgin Islands
580-584 Puerto Rico
585 NM
586 Guam, American Samoa, and Pacific Islands
587-588 MS
589-595 FL
596-599 Puerto Rico
600-601 AZ
602-626 CA
627-645 TX
646-647 UT
648-649 NM
650-653 CO
654-658 SC
659-665 LA
667-675 GA
676-679 AR
680 NV
681-690 NC
691-699 VA
700-728 Railroad workers through 1963
729-749 Unassigned for future use
750-751 HI
752-755 MI
756-763 TN
764-765 AZ
766-772 FL
773-799 Unassigned for future use
800-999 Not valid social security numbers