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Understanding the U.S. Social Security Number (SSN)

Social Security Numbers (SSN) in the United States are distributed by the Social Security Administration (SSA). Unlike in other countries where national identification numbers provide a wealth of information, such as Mexico or in the Balkans, an individual’s SSN may not contain a great amount of personally identifiable information (PII). However, it can provide the individual’s state of application or mailing address at the time they applied for a SSN that was issued prior to the implementation of SSN Randomization on June 25, 2011.

Social Security Numbers are made up of nine digits split into three sections: an area number (A), a group number (G), and a serial number (S). The format for SSNs is:


Area Number

For SSNs issued between 1936—when they were first introduced—and 1972, the three digit area number (A) corresponds to the state in which the individual applied for their SSN. Between 1972 and June 25, 2011, while the area numbers of the SSN still correspond to a state, they are based on the ZIP code of the individual’s mailing address when they applied for a SSN.

Group Number

The group number (G), or second set of digits, refers to the specific order in which SSNs are distributed within a geographical area from 01 to 99. First, odd numbers are assigned from 01 to 09 followed by even numbers from 10 to 98. Then, even numbers are assigned from 02 to 08. Last, odd numbers from 11 to 99 are assigned.

It is possible to determine if a social security number is valid using the SSA’s High Group History List. The SSA published the highest group number that is issued each month according to each area number. This means that any group numbers below the highest, according to the assigning pattern, are valid.

Serial Number

The final section, made up of four numbers, is assigned consecutively from 0001 to 9999.

This can be useful for validating a SSN or determining the state of an individual’s mailing address. While social security numbers are not readily available or able to be looked up, they may sometimes appear on older public documents.

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