Last Yellowstone eruption = 640,000 years ago. Six feet of ash in Nebraska and the Dakotas.
BTW, Yellowstone is 40,000 years over due for an eruption. If a 'Super-Volcano' goes off, don't bother running, you'll just die tired or starve.
Ping.
You are right about the last Yellowstone caldera eruption, but there was one a little more than 2 million years ago (I think the largest), and one around 1.3 mya. I am putting this from memory so the figures may not be exact.