Wyoming has no statewide residential code at all, so there is no state frost depth to look up: the number comes from whichever city or county you are building in, and in the parts of the state with no local code there is no adopted number to meet.
Wyoming leaves the frost line depth to the local building department, which is where the number for an address comes from.
Before a municipality or county without local enforcement authority is initially granted local enforcement authority for fire, building, existing building standards or electrical standards the state fire marshal shall determine that the local governing body has adopted minimum standards by ordinance or resolution that are equivalent to or more stringent than those applicable standards adopted by the department;Wyoming Statutes Title 35, Chapter 9, sections 35-9-106 and 35-9-121, Wyoming Legislature, read September 22, 2026. Read it at the source
That makes the building department issuing the permit the office with the number, and it is a short call: the counter gives the depth for the address, and the same call settles whether a deck footing or a slab edge needs a footing inspection before the concrete goes in. What Wyoming does publish is below, and it is worth having in hand first.
The air freezing index is the quantity the frost provisions of the model codes are written on: add up how far each day’s mean temperature fell below freezing over a winter, in degree days, and take the deepest run the winter managed. It measures how much cold the ground had to absorb, which is why it is the honest way to set one place beside another. Jackson is the coldest of the 3 cities on the record in Wyoming.
1,566degree days
average freezing index a winter
Jackson
| City | State | Freezing index | Once a century | Nights below freezing |
|---|---|---|---|---|
| Jackson | Wyoming | 1,566 | 2,874 | 241 |
| Casper | Wyoming | 783 | 1,699 | 182 |
| Cheyenne | Wyoming | 478 | 1,148 | 171 |
Computed from NOAA National Centers for Environmental Information, Global Historical Climatology Network daily temperature records for each station, from 1951 onward. These are measurements of winter, not depths.
Only a handful of states answer with one number for the whole state, and they are the only codes that can be set beside each other directly. Ranked by the freezing index at their own reference cities, with Wyoming marked at 942 degree days for comparison against what those codes settled on:
Left to right, the mildest winters to the hardest. The figure on the right is what that state wrote into its code.
The nearest by winter are Michigan at 42 inches, Vermont at 5 feet and Wisconsin at 4 feet. That is a reading of other states’ codes rather than a depth for an address in Wyoming: soil, drainage, snow cover and local amendments all move the figure, and the building department issuing the permit is the office whose number binds.
Wyoming code read September 22, 2026 from Wyoming Statutes Title 35, Chapter 9, sections 35-9-106 and 35-9-121, Wyoming Legislature. Codes are amended and a local amendment can be deeper than the state figure, so the building department issuing the permit has the number that binds. Every state is on the frost line depth hub.