A Social Security number (SSN) is a nine-digit identification number issued by the U.S. Social Security Administration (SSA) under Section 205(c)(2) of the Social Security Act. Although the SSN was originally created to track earnings for Social Security benefits, it has evolved into a core identifier used for taxation, employment, banking, and government services.
Understanding how Social Security numbers are assigned requires examining their structure, the historical numbering system, and the modern randomization process introduced in 2011.
The Structure of a Social Security Number
Every Social Security number follows the same nine-digit format:
AAA-GG-SSSS
Calculate Your 2026 COLA Increase →Each segment serves a specific administrative purpose:
- The first three digits are the Area Number
- The middle two digits are the Group Number
- The final four digits are the Serial Number
While these components once carried identifiable meaning, their significance changed after June 25, 2011, when the SSA adopted full randomization.
Area Number: The First Three Digits
How Area Numbers Were Assigned Before 2011
Before 1972, Social Security cards were issued by local SSA offices. The area number reflected the state where the card was issued, not necessarily where the applicant lived. Applicants could apply at any SSA office nationwide.
From 1972 until June 25, 2011, SSNs were issued centrally from Baltimore. During this period, the area number was based on the ZIP code listed on the original application’s mailing address. This address did not need to match the applicant’s actual residence.
Area numbers were assigned geographically, starting in the northeastern United States and moving westward. As a result:
- East Coast applicants generally received lower numbers
- West Coast applicants received higher numbers
This system was never intended to serve as meaningful geographic data. It existed solely to simplify paper-based record storage in an era before computers.
Area Numbers After SSN Randomization (Post-2011)
On June 25, 2011, the SSA implemented SSN randomization, which eliminated the geographic significance of area numbers. Since then:
- Area numbers are assigned randomly
- They no longer indicate state, region, or ZIP code
- Previously unused numbers in the 700s and 800s were introduced
Certain numbers remain permanently excluded:
- 000
- 666
- 900–999 (reserved for Individual Taxpayer Identification Numbers)
Anyone receiving an SSN after June 25, 2011 has a number that cannot be decoded for location or timing.
Group Number: The Middle Two Digits
The group number ranges from 01 to 99 and was never assigned consecutively.
Historical Group Number Assignment Pattern
For administrative tracking, the SSA issued group numbers in a specific non-linear order within each area number:
- Odd numbers from 01 through 09
- Even numbers from 10 through 98
- Even numbers from 02 through 08
- Odd numbers from 11 through 99
This pattern allowed the SSA to monitor number usage internally. Group number 98, for example, would be issued before group 11.
The group number does not represent:
- Age
- Gender
- Citizenship
- Employment status
After SSN randomization, group numbers no longer follow this historical pattern and are assigned randomly.
Serial Number: The Last Four Digits
The serial number identifies individuals within each area-group combination.
- It runs consecutively from 0001 through 9999
- It contains no personal data
- It simply ensures uniqueness within the assigned block
Despite common belief, the last four digits do not encode any personal information. They are often used for partial identity verification because they are the least predictable portion of the number.
How Social Security Numbers Are Assigned Today
The SSA currently assigns SSNs using a fully randomized system:
- All eligible numbers are randomly generated
- Geographic and chronological indicators are removed
- Predictability is reduced to limit identity fraud
- The total pool of available numbers is expanded
Randomization applies to:
- New SSNs
- Replacement SSNs issued after June 25, 2011
Even individuals who had SSNs issued before 2011 receive randomized numbers if a replacement is approved.
Why the SSA Changed the Assignment System
Preventing Identity Theft
Before 2011, criminals could reconstruct likely SSNs using publicly available data such as place of birth and application timing. Randomization removed this vulnerability.
Preventing Number Exhaustion
Under the old system, several high-population states were projected to run out of available numbers. Randomization expanded the pool to more than 400 million usable combinations.
Adapting to the Digital Age
The original system was designed for filing cabinets and paper records. Random assignment aligns better with modern digital infrastructure.
Numbers That Are Never Issued
The SSA permanently excludes certain SSNs:
- Any number with all zeros in one segment
- 000-xx-xxxx
- xxx-00-xxxx
- xxx-xx-0000
- Numbers beginning with 666
- Numbers beginning with 900–999
Social Security numbers also have no check digit, unlike many financial identifiers.
Are Social Security Numbers Reused?
No.
The SSA does not reuse SSNs under any circumstances, including after death. Since 1936:
- Over 540 million SSNs have been issued
- The SSA averages more than 6 million new numbers annually
- The system is projected to last for generations without expansion
Duplicate numbers have occurred only through administrative errors or misuse, not intentional reassignment.
Applying for a Social Security Number
SSNs are obtained by submitting Form SS-5. As of March 2026:
- Automatic issuance through USCIS forms has been suspended
- All applicants must attend in-person SSA appointments
- Enumeration Beyond Entry (EBE) is no longer active
An SSN is permanent and does not expire, even if work authorization does.
Who Can Receive a Social Security Number
SSNs are issued to:
- U.S. citizens by birth or naturalization
- Lawful permanent residents
- Non-citizens authorized to work
- Certain non-working individuals who need an SSN for federal benefits
Some cards carry employment restrictions, such as:
- “Not valid for employment”
- “Valid for work only with DHS authorization”
Can a Social Security Number Be Changed?
The SSA approves SSN changes only in limited situations:
- Ongoing identity theft causing harm
- Domestic violence or harassment
- Duplicate numbers
- Religious objections to specific number sequences
Credible third-party documentation is required.
Key Takeaways
- Social Security numbers consist of three parts: area, group, and serial
- Before 2011, numbers followed a geographic and administrative pattern
- Since June 25, 2011, all SSNs are assigned randomly
- SSNs are permanent, unique, and never reused
- The assignment system prioritizes security, longevity, and administrative efficiency
How Are Social Security Numbers Assigned?
Social Security numbers are assigned randomly by the Social Security Administration.
Before 2011, numbers followed a structured geographic and administrative system. Today, all eligible nine-digit combinations are randomly generated, excluding prohibited ranges, to protect against fraud and ensure the system remains viable for future generations.
