High Quality Content by WIKIPEDIA articles! The U.S. state of Kansas first required its residents to register their vehicles and display license plates in 1910. Kansas has a system of county codes used for identification of the home county of a state resident or company on license plates and state tax forms. The codes are two letters based on the first letter of and another letter in the name of the county. There is no true convention for the selection of the letters; for example, Bourbon County is the only county that begins with "BO," yet its code is "BB." In most cases, but not all, as noted above, the only county that begins with two particular letters gets those letters. Exceptions are Decatur, Dickinson, Hodgeman, Leavenworth, Logan, McPherson, Norton, Pawnee, and Pottawatomie.