Does Idaho have a volcano?

Yes. (Four) All inactive.
1. Shoshone (North of Twin Falls)10,000 years ago
2. Craters of the Moon (South West of Arco) Was created by 8 eruptive episodes from 15,000 years ago to 2000 years ago.
3. Wapi Lava Field (SE of Craters of the Moon) Erupted 2500 years ago
4. Hell' Half Acre (10 miles North of Blackfoot by I15) Erupted 5200 years ago.
Note: There is a large amount of lava beds and cinder buttes that run in a south westerly direction from Rexburg & Dubois, Idaho to just west of Twin Falls, Idaho along the Snake River plain.
Note: Although the majority of Yellowstone National park is not in Idaho, it is worthy to note that Yellowstone National Park is filled with geyers and hot pools and is on a huge inactive volcano called a caldera, which is 34 by 45 miles wide. The Yellowstone area experiences between 1000 and 2000 measurable earthquakes a year, mostly under 3 . Yellowstone National Park was formed from 3 huge volcanic explosions that took place 2.1 million to 640,000 years ago. This inactive volcano has helped create all of the lava beds and cinder buttes that run south westerly along the Snake River plain into Nevada.