U.S. currency is designed to prevent counterfeiting and manage the tracking of the loose bills. Each bill printed in the United States contains a lot of information about where and when the bill originated. The $1 bill lists a few sets of numbers, including the series, serial and plate serial numbers. These all provide different information that is useful to banking professionals.
TL;DR (Too Long; Didn't Read)
The series number on a dollar bill identifies the year when the design of the bill was implemented, rather than when the bill was actually printed.
Bill Series Number
The series number on a dollar bill is found between the image of President George Washington and the signature of the Treasury secretary. However, it may appear on the left of the image for bills of greater denomination or that have been printed more recently. The series number is actually a year, such as 1995 or 2010, with the word "series" written above it. A letter can also be added after the year for some series.
However, the series number doesn't necessarily indicate the year the bill was physically printed. Each year does not have a series of dollar bills, as new series are only issued when a change is made to the bill.
Bill Design Changes
New series of dollar bills are issued when there are changes to the design of the bill, a new secretary of the treasury or a new treasurer of the United States. The treasurer and secretary's signatures appear on the bills, so a new series is created when someone new takes office.
A new treasurer of the United States results in a series number in the form of the year followed by a letter. For example, 2010A might be a series number in that situation. Changes to the bill's design or a new secretary will generate series numbers that are only the year.
Bill Serial Numbers
Serial numbers printed on dollar bills are not unique to each bill. A bill's serial number comprises a starting letter, followed by a series of numbers and an ending letter. The starting letter indicates the Federal Reserve Branch that printed the bill. The ending letter tracks how many times the specific series of numbers were used.
A specific series of numbers can be used 26 times – once for each letter of the alphabet. Bills are printed in sheets of 32 with identical serial numbers. The serial number of a dollar bill is found in two locations on the front of the bill – the upper right section and the lower left section.
Plate Serial Numbers
The engraving plates used to print paper money are also designated by serial numbers. This number is printed on the front side and the back side of bills. On the front of a $1 bill, it is located to the right of the word "one" on the right side of the bill. It is also on the right side on the back of the dollar bill, below the word "one." This number is a capital letter with smaller numbers printed after it.
In conjunction with the plate serial number is the plate position number. The plate position number shares the same letter as the plate's serial number, followed by a digit 1 through 32, because there are 32 bills printed per plate.