What Are Serial Numbers?
Learn the structure of serial numbers on U.S. paper money, how district letters work, and why they matter to collectors.
Serial numbers are the unique identification codes printed on every U.S. paper currency note. They serve a critical function in tracking, accounting, and detecting counterfeit currency. Understanding serial numbers is the foundation of currency collecting.
The Basic Structure
A serial number on a modern U.S. Federal Reserve Note consists of:
- One prefix letter (the first character)
- Eight digits (0-9)
- One suffix letter (the last character)
For example: A12345678B
The Prefix Letter: Federal Reserve District
The first letter indicates which of the 12 Federal Reserve Banks issued the note. This letter is called the district letter. The 12 districts and their letters are:
- A – Federal Reserve Bank of Boston
- B – Federal Reserve Bank of New York
- C – Federal Reserve Bank of Philadelphia
- D – Federal Reserve Bank of Cleveland
- E – Federal Reserve Bank of Richmond
- F – Federal Reserve Bank of Atlanta
- G – Federal Reserve Bank of Chicago
- H – Federal Reserve Bank of St. Louis
- I – Federal Reserve Bank of Minneapolis
- J – Federal Reserve Bank of Kansas City
- K – Federal Reserve Bank of Dallas
- L – Federal Reserve Bank of San Francisco
The Eight Digits: Sequential Numbering
The eight digits represent the sequential order in which the note was printed within that particular print run. Each note receives a unique number, starting from 00000001. When a run reaches 99999999, a new prefix letter or new series begins.
The Suffix Letter: Plate Designation
The final letter (usually A through Z) indicates which printing plate was used for the reverse (back) of the note. Different plates may be cycled through during large print runs to manage wear on engraving plates.
Star Notes
Occasionally, the suffix letter is replaced with a star symbol (★). This designates a replacement note printed to replace a defective note discovered during quality control. Star notes are discussed in detail in the Star Notes section.
Why Serial Numbers Matter
Serial numbers allow the Bureau of Engraving and Printing to:
- Track production quantities by date and district
- Identify counterfeits by checking sequential gaps
- Account for all printed currency
- Manage inventory and distribution
For collectors, serial numbers are the primary way to identify and assess the rarity of a note. Many collecting specialties revolve around interesting or rare serial number patterns.
Ready to put this to use?
Bill Bounty hunts involve real circulating U.S. currency. Apply what you've learned to spot target bills in the wild.