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My grandfather on my mother’s side is named Joseph. His son is also named Joseph. Not Joseph Junior. Not Joseph II. Just Joseph. They’re both just Joseph [Last Name], which sometimes makes traveling with them a headache. Not long after 9/11, the lot of us went on vacation together and got held up in security whenever the TSA took issue with the fact that two different guys with the same name were booked for the same flight.

This is the kind of issue that the Social Security Administration was hoping to avoid when it began to track the earning histories of U.S. workers and determine their Social Security entitlement and benefit levels in the early 1930s. Names on their own, or partnered with addresses, wouldn’t work as identifiers for people when guys like my grandfather passed on their names to their sons, but neglected to tack on a “Junior.” While that sort of situation might not be common, how many unrelated Joe Smiths have you met in your life? In a 5-second web search, I found 4,513 in the U.S., and that probably doesn’t cover all of them. What’s more, there’s the problem of people changing their names and moving from address to address.

Some government agencies like the War Department and the Veterans Administration used fingerprints to ID people, but fingerprinting is associated with being arrested and booked in the public mind, and the SSA decided that people weren’t going to have it. Eventually, they hit upon the idea of using numbers as unique identifiers, and the Social Security Number was born.

Figuring out the Format

Initially, the number was going to consist of three alphabetic characters and five numeric characters. Only two companies at the time manufactured tabulating machines that used alphabetic characters, though, and the federal government had previously gone after them under antitrust legislation for dividing the market between them. The SSA didn’t want to turn around and give them government business, so a new, letter-free numbering scheme had to be worked out.

They considered a few different options and settled on a 9-digit number consisting of a 3-digit geographic code, a 2-digit age indicator and a 4-digit serial number. The 2-digit code was to represent the year that number’s owner reached the retirement age, and after that, their number could be recycled. That plan was scrapped when someone suggested that tying the number to age would encourage people to falsify their age when applying for a number.

In the summer of 1936, the SSA finalized the 9-digit number scheme, with the fourth and fifth digits acting as a “group number” that would be assigned in a specific sequence and allowed for the pre-numbering of registration forms.

SSN Structure

From then on, the SSN consisted of three parts: area number, group number and serial number.

The first three digits are the area number, which is assigned by geographic region. Area numbers were assigned to each state based on the anticipated need for SSNs to be assigned in them. The numbers were generally doled out in ascending order beginning with the Northeast states (but not with the most northeast of them, as we’ll learn soon) and then moving south and west—so, theoretically, a person’s number could give the SSA some information about where that person lived, enabling them to track geographic trends in benefit distribution. This never really worked out for them.

At first, the area numbers were issued to local post offices—the SSA didn’t have their own field offices yet—to assign to people, but some large companies with multiple offices, branches or stores across the country had all of their employees send their SSN applications to their national headquarters for central processing and mailing. If you worked at a bank branch in California, but the home office was in New York, your number wound up not reflecting your place of residence and didn’t tell the SSA anything useful. Later, the SSA started assigning SSNs centrally from their Baltimore office based on the ZIP code of the mailing address people put on their applications. This didn’t work out either, since someone’s mailing address doesn’t necessarily reflect where they live or work.

Some exceptions to the geographic distribution were made. Numbers 700-728, for example, weren’t assigned by region, but were reserved for railroad workers until 1963. Numbers 587-595 went to Mississippi and Florida, out of order, after the two states used up their initial runs of numbers. SSNs with the area number 000 or 666 have never, and likely won’t ever, be assigned.

Last year, the SSA decided to do away with the geographical significance of the first block of digits, and is no longer assigning them to specific states.

The second group of digits is the group number. Contrary to conspiracy theory and urban legend, these don’t reflect racial or ethnic groupings. The “group” just refers to the numerical subgroups into which the area numbers are broken down. The reason for doing this was so that early SSA administrators could break down their files into smaller, more manageable, subgroups, which allowed them to find information more easily. These groups range from 01 to 99 and are issued, within each area number, in this order: odd group numbers from 01 to 09; even numbers 10 to 98; even numbers 02 to 08; and odd numbers 11 to 99.

The last four digits are the serial number, a straight numerical series of numbers from 0001–9999 within each group.

With the number scheme figured out, the SSA was ready to start assigning numbers to the public. We’ll find out who the first social security number went to tomorrow.