Idaho license plate codes start with a county identifier: a letter that matches the first letter of the county where the vehicle is registered, paired with a number when more than one county shares that letter. Ada County plates open with 1A, Adams County with 2A, Bannock with 1B, and so on. Where only one county in Idaho starts with a given letter, the number is dropped and a single letter does the job.
How the County Prefix Works
The prefix is not random. The letter tells you the county’s initial, and the number ranks counties that share that initial, generally in order of population or historical assignment. Ada County, home to Boise, carries 1A because it’s the first “A” county. Adams County follows as 2A. On the “B” side, Bannock County is 1B, Bear Lake is 2B, and Bonneville County, which includes Idaho Falls, is 8B.
When a letter belongs to only one county, Idaho skips the number. Kootenai County plates simply start with K. Nez Perce plates start with N. Shoshone is S. Elmore is E. That single-letter shorthand is a quick tell that no other county in the state competes for that initial.
County Codes Across Idaho’s 44 Counties
Idaho has 44 counties, and each has its own designator built on the same pattern. A handful of common examples:
- 1A — Ada County (Boise)
- 2A — Adams County
- 1B — Bannock County
- 2B — Bear Lake County
- 8B — Bonneville County (Idaho Falls)
- 2C — Canyon County
- E — Elmore County
- K — Kootenai County (Coeur d’Alene)
- N — Nez Perce County
- S — Shoshone County
- 2T — Twin Falls County
Longtime Idaho residents often read a plate’s home county at a glance, and law enforcement uses the prefix to identify quickly where a vehicle is registered.
What the Rest of the Plate Tells You
After the county code comes a sequence of letters and numbers that uniquely identifies the individual vehicle. The plate’s overall design tells you what kind of vehicle it is and whether the owner has chosen a specialty or organizational plate.
Standard Passenger Plates
Most Idaho drivers carry a standard passenger plate. It shows the county prefix followed by the unique letter-and-number sequence. These plates are issued to private passenger vehicles, with registration fees governed by Idaho Code 49-402 and set based on factors like the vehicle’s age and type.
Specialty Plates
Idaho also issues specialty plates that let owners support causes or show affiliations. Wildlife conservation plates come in Bluebird, Elk, and Cutthroat Trout designs. A new wildlife plate costs $35 on top of standard registration fees, with $25 renewals; personalized versions run $60 initially and $40 to renew. Other categories include university plates, veterans’ plates, and organizational designs, each with its own added fee.
Commercial Vehicle Plates
Commercial plates are separate from passenger plates and follow a fee schedule tied to weight. Under Idaho Code 49-434, a commercial vehicle weighing between 8,001 and 16,000 pounds pays $48 per year, while one in the 50,001-to-60,000-pound range pays $515.40. Vehicles over 60,000 pounds use a formula that combines weight with total miles driven on Idaho roads, with fees running from $223 at the low end up to $5,860 for vehicles over 128,000 pounds driving more than 50,000 miles a year.1Idaho State Legislature. Idaho Code Section 49-434 – Operating Fees
The Validation Sticker
The small color-coded sticker on the plate is not part of the county code. It carries a number from 1 through 12 that corresponds to the month the registration expires, so a plate with a “7” sticker expires in July. Recreational vehicle registrations are the exception: they all expire on December 31.2Idaho Transportation Department. Vehicle Registrations
Why the System Exists
The county-prefix system predates modern computer lookups and gives officers, clerks, and other drivers an immediate read on where a vehicle is based. Because the letter tracks the county name and the number reflects a fixed ranking, the codes are stable over time. A 1A plate has always meant Ada, and a K plate has always meant Kootenai, regardless of the vehicle behind it.
Put the pieces together and any Idaho plate breaks down the same way: a county prefix (one letter, or a number plus a letter), a unique alphanumeric sequence identifying the vehicle, a plate design signaling standard, specialty, or commercial status, and a month sticker showing when registration expires. Once you know which piece is which, an Idaho plate reads like a short sentence about the vehicle.