The United States, does not have national identification cards. Instead, in the 1930s, the Social Security Administration (SSA) was created, and the federal government mandated that all legal residents and citizens must have a valid social security card.

The Social Security Administration issues these numbers to applicants who meet their criteria. A Social Security number contains nine digits: the first three digits are related to the Zip Code for the area you live in when you first apply for your card; and the last four digits are in numerical order of being assigned from 0000 to 9999.

The middle two numbers are called group numbers and are not assigned consecutively, but instead in groups of odd and even (02 and up for even; 01 and up for odd). Group numbers are allocated for each state.