Social Security isn't just about benefits for retirees, the disabled, and their families. It's become so enmeshed in the American society that it has become a key part of people's identity. Indeed, now that smartphones have made memorizing your phone number largely a thing of the past, the first number many people commit to memory is their Social Security number.

Your unique number isn't just important for receiving Social Security benefits. The IRS uses Social Security numbers for most taxpayers in tracking tax returns and reporting. Financial institutions gather it when you open bank accounts or want a loan.

Given how ubiquitous Social Security numbers are, it's not surprising that many people wonder if there's any meaning behind what your particular Social Security number is. And as it turns out, for more than 75 years, there were indeed some little-known codes that went into determining how a new Social Security number got assigned. Here's the secret behind what your Social Security number means -- and why the federal government changed how it assigns new numbers to eliminate this hidden meaning going forward.

Brass key on top of four Social Security cards.

Image source: Getty Images.

The hidden codes in your Social Security number

One of the first challenges that the government faced after the Social Security Act became law in 1935 was how to assign unique identifiers for every American entitled to benefits. At the time, nine-digit numbers were more than adequate to handle the U.S. population of between 125 million and 130 million.

The first three digits of the Social Security number represented a specific area number. Each U.S. state, territory, and possession had one or more area numbers assigned to it. So when a person went to a Social Security office to apply for a Social Security number, the area number of that office went into the number. By the 1970s, all new number issuances got handled at a central office, so the area number represented the state of residence indicated on the application. Special area numbers initially applied to railroad workers covered by the separate Railroad Retirement Act system.

In general, if you're familiar with the way postal zip codes get assigned, the area numbers will look familiar. Low numbers start in New England and the Northeast, and numbers typically got higher as you went southward and westward. Yet because the initial numbers only went up to the 500s in most cases, zip codes and area numbers rarely matched up exactly. Moreover, as some areas used up their numbers, new ones got added.

The middle two digits of Social Security numbers were the group number. This didn't indicate any sort of demographic group but rather simply indicated the order in which numbers got assigned. The first group numbers were odd numbers between 01 and 09, followed by even numbers from 10 to 98, even numbers from 02 to 08, and odd numbers from 11 to 99.

Finally, the last four digits of the Social Security number indicated a strict chronological order within the area and group. The lower the number, the earlier in the group the number got assigned.

Why new Social Security numbers don't mean anything

Modernization led the Social Security Administration to change its methodology for assigning new Social Security numbers in 2011. Now, the SSA randomly assigns Social Security numbers, subject to certain rules and validation procedures.

The move came for several reasons. Randomization allowed the SSA to make better use of available numbers. It also offered some identity protection benefits, although it did force a change in the long-established way that financial institutions and other users verified whether a Social Security number was legitimate.

As a result, today's preteens and younger children won't be able to find any hidden meaning within their Social Security number. For teenagers and adults, however, it's worth taking a minute to look at your Social Security number and think about what those digits say about your personal history.