High Quality Content by WIKIPEDIA articles! The U.S. state of Ohio has issued license plates since 1908. With the exception of the World War II years, the passenger number plates were issued in pairs. Starting in 1935, a county coding scheme involving the letters in the plate's serial number was introduced. This scheme was used throughout the state until the 1970s, when the system broke down in the most populous counties because of the number of vehicles registered in them. The coding scheme was abandoned with the issuance of the 1982 plates. Today, there is a county coding scheme on a sticker that displays the county number based on its placement in alphabetical order.