The 9-Digit Number That Changed America’s Identity

Over 90 years, the Social Security number has evolved from a code to track earnings into the passkey to our financial lives

Jon Marcus,

AARP

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En español

Published June 13, 2025

figures walk across a floor of social security cards

Rob Dobi

Fingerprints. Dog tags.

That’s how 1930s critics of the newly established Social Security system claimed the federal retirement benefit program would track American workers.

It was mostly political hyperbole. But devising an acceptable way of individually identifying the millions of workers who would pay into and, ultimately, collect Social Security proved a challenge so vast that even the man assigned to do it thought it was impossible.

“No one in the world had ever done a huge task like this. They had to invent it as they went,” says Nancy Altman, president of the advocacy group Social Security Works and author of The Battle for Social Security, a history of the program. “The idea of enumerating that many people was a massive job. And they had to do it right away.”

The result was the nine-digit Social Security number, or SSN, an innovative solution so sturdy it has not only sustained the vast Social Security system but also spread to other government agencies and the private sector, becoming the de facto national ID.

“It was definitely ingenious,” says Rahul Telang, a professor of information systems at Carnegie Mellon University. “In a very simplistic way, they were able to come up with a number that was really robust.”

How this happened is a tale of political intrigue, bureaucratic dedication, a largely forgotten management consultant and a data file with the ominous name of Numident. It’s a story still being written, as the SSN’s evolution into the passkey to our financial lives makes it a potent tool for scammers and identity thieves that could eventually give way in some spheres to biometric identifiers such as … fingerprints.

a colorful poster advertising social security as a monthly check to you

As Social Security ramped up in 1936 and ’37, the government printed posters encouraging workers to sign up for the program — and the new number that went with it.

SSA History Archives

Filibusters and ‘fearmongering’

President Franklin D. Roosevelt signed the Social Security Act on August 14, 1935. The law set a January 1937 deadline to start collecting payroll taxes from the first 26 million workers covered by the program. That gave the Social Security Board — the precursor to today’s Social Security Administration (SSA) — less than a year and a half to hire thousands of employees, create a national network of offices and figure out the many details of the program from scratch.

Foremost among these was finding a way to accurately track people’s earnings across their working lives and store that information in a way that allowed fast, easy retrieval. That would require a universal form of identification, something Americans had never had.

The work was complicated by politics. A filibuster by populist Louisiana Sen. Huey Long blocked a budget bill that included start-up funds for Social Security. Roosevelt responded by shifting money and staff from other federal departments. Republicans, including Alf Landon, FDR’s opponent in the 1936 presidential race, stirred suspicions that Social Security would require workers to wear dog tags or be fingerprinted.

“It was fearmongering,” says Altman.

In truth, fingerprinting was considered but quickly shot down; while a few government agencies at the time used fingerprinting for ID purposes, Social Security officials feared it would make people feel like criminals. Simply using names and addresses was impractical in an era when more people shared the same conventional names.

According to Altman, the board calculated that there were hundreds of thousands of workers nationwide with common surnames such as Smith, Jones, Brown and Miller. “You’d need to know where all of these John Smiths worked, and every week you’d have to input what each of these John Smiths had earned,” she says.

A code of some kind would be needed. The first attempt was an eight-character string, three letters followed by five numbers, according to a 2009 SSA research paper on the process. This offered many hundreds of millions of potential combinations, but it had an important limitation: Few of the statistical machines then in use — essentially, analog computers that analyzed permutations of numbers — could process letters.

‘It was impossible’

With the clock ticking, the board called in a consultant. In his memoir on the program’s formative years, Arthur Altmeyer, an original member of the board and later the Social Security commissioner, outlined this person’s contributions but did not give a name. Altman, in researching her book, was able to identify him (via an in-house SSA historian) as Harry Hoff, an expert on office layout and management who came recommended by several large insurance companies from which the board sought help.

Hoff was assigned to find an enumeration system that would provide a distinct identifier for hundreds of millions of people, “in a format that wasn’t too cumbersome but in a way that you wouldn’t run out of numbers,” Altman says. After studying the matter for several months, she says, he “came back and said it was impossible.”

The board told him to keep working, and he ultimately cracked the code. The board approved his proposed nine-digit system on June 2, 1936.

The first three digits would represent where the SSN was issued, with states divided into “area numbers” that, in general, got higher going from East to West (000, 666, and the 800s and 900s were excluded). Next came a “group number” from 01 to 99, an administrative designation to break numbers within an area into blocks for filing and processing. Within each group, workers got a “serial number” — the “last four digits” now used as an identification check on customer service calls everywhere.

Nearly a billion combinations of this nine-digit number would be available without duplication. According to SSA statistics, about half a billion have been used so far.

The methods of assigning and issuing numbers would be tweaked over the years. For decades, railroad workers had their own starting sequence — 700 to 728 — but that practice ended in 1963. In the 1980s, the SSA began rolling out “enumeration at birth,” allowing parents to request SSNs for newborn babies at the hospital.

The biggest change came in 2011, when the SSA abandoned geographic coding for the first three digits and added previously unassigned numbers to expand the pool of available numbers. (There were still plenty of nine-digit combos, but some faster-growing states were in danger of exhausting their fixed area numbers.) Since then, all new numbers have been assigned randomly, from the first digit to the last.

Postal workers to the rescue

As ingenious as the Social Security number was, there was no guarantee that Americans would embrace it or that the fledgling agency could stand up the system in time.

Thanks in part to the filibuster-fueled funding delay, the Bureau of Old-Age Benefits, as the body charged with registering workers was known, still had only five employees in March 1936, including its director. With Landon vociferously campaigning against Social Security, many Americans were suspicious of this new bureaucracy.

The agency turned to some of the most trusted government employees: the postal carriers who visited every house in the country, almost every day. They would distribute and collect applications for SSNs, so “you weren’t giving your personal information to a faceless stranger,” Altman says. Post office workers were even enlisted to type up the new Social Security cards.

To further promote participation, the government went on a publicity blitz, distributing millions of posters and pamphlets encouraging workers to apply for their numbers, organizing national radio broadcasts and even producing a film trailer.

As a gesture of thanks to former New Hampshire Gov. John Winant, a Republican who crossed party lines to serve as chairman of the Social Security Board, the first area number, 001, went to New Hampshire rather than Maine, the logical geographic choice. This was part of a plan to ceremoniously assign Winant the “first” SSN, 001-01-0001, but he turned it down.

After a few other dignitaries did the same, the number was quietly issued to Grace Owen of Concord, New Hampshire, whose application was the first processed in the 001 area as post offices started distributing Social Security cards in November 1936.

That number, and those that followed, went into master files at Social Security headquarters, then in downtown Baltimore. They were stored on punch cards and paper until the 1970s, when the SSA, by then based in the Baltimore suburbs, transferred the data to an electronic Numerical Identification System, or Numident, the digital repository still in use today.

John Winant during his tenure on the Social Security Board. The former New Hampshire governor turned down an offer to get Social Security number 001-01-0001.

SSA History Archives donated by Maurine Mulliner

A ‘unifying number’

While the Social Security number was created to serve the Social Security program, other government agencies soon started using it, and financial institutions followed suit.

“It started to evolve over time to be more than what was originally intended, which was just for tracking work history and earnings,” says Nick Bour, a retirement planning adviser and CEO of Inspire Wealth in Brighton, Michigan.

The evolution began with a 1943 executive order that required other federal agencies to start using SSNs to identify people in their record systems. It sped up in 1962, when the IRS started using them for federal tax reporting. Medicare adopted the SSN, too, when it was established in 1965.

A 1970 law required banks and other financial institutions to obtain customers' Social Security numbers; another, in 1976, ordered that states collect them for taxes, drivers’ licenses and motor vehicle registrations. Even the Census Bureau uses SSN-linked tax data to compile population estimates (although it will never ask for your Social Security number).

Being able to use customers’ SSNs saved these and other businesses and government departments the time and cost of developing their own identification systems, Telang says: “It became a nice unifying number, where if I have access to that particular number, I can connect the user across different domains, even though that was never the intention.”

There was a benefit for consumers, too: Without widespread adoption of the SSN, he says, “you would have so many numbers — one for the mortgage, one for the bank. That didn’t work. So, this became the default.”

Not everyone was on board, including the SSA. As early as 1971, an agency task force warned against promoting the number as a national identifier, urging a “cautious and conservative” approach. But Congress kept doing it anyway, making Social Security numbers a prerequisite for accessing numerous government benefits.

“Back in the ’70s, we didn’t really have the technology and issues we have now” with data breaches and identity fraud, says Bour. As those dangers have grown, the government has somewhat scaled back its reliance on SSNs.

For example, Congress, citing the risk of identity theft to older Americans, passed legislation in 2015 to remove Social Security numbers from Medicare cards and replace them with a new number, the Medicare Beneficiary Identifier. Several state legislatures have also stepped in to limit the use or display of Social Security numbers.

Telang predicts that non–Social Security uses of Social Security numbers by everything from credit trackers to health plans will be replaced over time by biometric identification, such as facial, iris, retina or fingerprint recognition. That way, he says, “the ‘number’ is you. Nobody can steal it.”

Still, those nine digits continue to serve for their original purpose: ensuring that when you retire or suffer a disability, the government has the information it needs to pay the benefit you’ve earned.

“We don’t think about it,” Altman says. “You start a job and all you give the government is your Social Security number, and when you’re 65, it’s all been kept.”

The bureaucrats who made this possible “were unbelievably dedicated and hardworking and visionary,” she says, “and recognized how important the job was that they were doing.”

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Jon Marcus is a Boston-based writer whose work appears in The New York Times, The Washington Post, USA Today, The Boston Globe and other media outlets.