Serial Numbers

The first letter of such a serial number identifies the Federal Reserve Bank (FRB) which issued the note; since there are 12 FRBs, this letter is always between A and L.  The last letter advances through the alphabet when all eight character serial numbers have been printed for a specific Federal Reserve Bank within the same series.  At the time of a series change, the suffix letter returns to the letter A and repeats the cycle.

The letter O is not used because of its similarity to the digit 0, and the letter Z is not used because it is reserved for test printings.  On some notes, a star appears in place of the last letter.  When an imperfect sheet is detected during the manufacturing process after the serial number has been overprinted, it must be replaced with a new sheet.  A "star" sheet is used to replace the imperfect sheet.  Reusing an exact serial number to replace an imperfect note is costly and time consuming.  A "star" note has its own special serial number followed by a star in place of a suffix letter.

Federal Reserve notes, beginning with Series 1996, have two letters rather than one at the beginning of the serial number.  On these notes, the first letter corresponds to the series of the note and the second letter of each serial number now represents the issuing FRB and ranges from A through L.  The last letter still can be anything but O or Z, and is still occasionally replaced by a star, with the same meaning as before.
 

Serial Numbers - Series Year and Serial Number Relationship Table

* The prefix letter on the serial number for denominations $5 and higher indicates the note series.  It changes whenever the series year or series year suffix letter changes.  This prefix letter was added to the serial numbers on $5 and higher notes starting with Series 1996.  The $1 and $2 notes do not have this prefix letter.

Serial numbers - Federal Reserve Bank and Serial Number Relationship Table