The nine-digit Social Security Number (SSN) is composed of three parts:
- The first set of three digits is called the Area Number
- The second set of two digits is called the Group Number
- The final set of four digits is the Serial Number
The Area Number is assigned by the geographical region. Prior to 1972, cards were issued in local Social Security offices around the country and the Area Number represented the State in which the card was issued. This did not necessarily have to be the State where the applicant lived since a person could apply for their card in any Social Security office. Since 1972, when SSA began assigning SSNs and issuing cards centrally from Baltimore, the area number assigned has been based on the ZIP code in the mailing address provided on the application. The applicant's mailing address does not have to be the same place as their residence. Thus, the Area Number does not necessarily represent the State of residence of the applicant, either prior to 1972 or since.
Generally, numbers were assigned beginning in the northeast and moving westward. So people on the east coast have the lowest numbers and those on the west coast have the highest numbers.
Within each area, the group numbers (middle two digits) range from 01 to 99 but are not assigned in consecutive order. For administrative reasons, group numbers issued first consist of the ODD numbers from 01 through 09 and then EVEN numbers from 10 through 98, within each area number allocated to a State. After all numbers in group 98 of a particular area have been issued, the EVEN Groups 02 through 08 are used, followed by ODD Groups 11 through 99. These numbers do not really provide any clues for genealogy purposes.
Group numbers are assigned as follows:
- First: ODD - 01, 03, 05, 07, 09
- Second: EVEN - 10 to 98
- Third: EVEN - 02, 04, 06, 08
- Fourth: ODD - 11 to 99
Within each group, the serial numbers (last four (4) digits) run consecutively from 0001 through 9999. These also have no bearing on genealogy research.