U.S. States with Glaciers

If the border with Wyoming was 15 miles to the east, Idaho would have several (small) glaciers in the Teton Range. As it is, the American Rockies just don't have very much in the way of glaciers to begin with. They are too dry, and tend to not be quite high enough to hit the snowline except in sheltered places, and that does not really change as you go north until you reach the Canadian Rockies. The only serious large scale glaciation in the American Rockies is in the Wind River Mountains of Wyoming. So it isn't surprising that one state would lose out.

I would guess that Idaho loses out as its mountains are mostly on the drier west side of the Rockies, its highest peaks run in narrow ranges that run north-south and provide little in the way of permanent shade in high elevations that might allow glaciers to form lower than usual. Its highest mountains are also further south, in the driest parts of the state, while wet northern Idaho has mountains that barely get above treeline.

It looks like they had one but it melted. Sad.

Honestly, if the rock glacier on Timpomagos in Utah is included, then Idaho should be included as well. While Idaho has at best one true glacier, there are a ton of rock glaciers in the Sawtooth Mountains in Idaho. Worth pointing out that "Rock Glacier" != a regular glacier that is just covered in rocks. While they can be that, they don't have to be. There might be no actual ice underneath there at all, just permafrost that is slowly deforming under the force of gravity, having more to do with mass-wasting or landslides than true glaciers. Now the rock glacier in Utah is arguably more like a real glacier in that it clearly has an ice core, I would not be surprised if at least one rock glacier in Idaho also has an ice core.

Source on Idaho:https://glaciers.us/glaciers.research.pdx.edu/Glaciers-Idaho.html