Vehicle registration plates of Idaho

The U.S. state of Idaho first required its residents to register their motor vehicles and display license plates in 1913.

In 1956, the U.S. states and Canadian provinces came to an agreement with the Automobile Manufacturers Association that standardized the size for license plates for vehicles, except those for motorcycles, at six inches in height by twelve inches in width, with standardized mounting holes. The 1956 (dated 1957) issue was the first Idaho license plate that fully complied with these standards: the issues from 1952 through 1955 (dated 1953 through 1956) were all six inches in height by twelve inches in width, but had non-standard mounting holes.

The following county codes have been used on standard-issue Idaho license plates since 1945. The naming convention is the order of the county in an alphabetical list followed by the first letter of the county name. For example, 2T indicates the second county beginning with T in an alphabetical list, or Twin Falls County. If only one county begins with a particular letter, the letter alone serves as the county code. Specialty and vanity license plates do not use county codes; some non-passenger types are county-coded, while others are not.

Since the introduction of this design, the plate has been colloquially referred to by Idahoans as the "nuclear winter" plate. It remains so to this day (with the most recent 2008 design retaining the characteristic features).

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