Nature sleuth, Barb, helped us identify it as a Crecopia Moth Caterpillar. This means it will become the largest moth in North America! We have discovered that it likes maple leaves and buckthorn. It should spin a cocoon soon, and then we'll have to wait until spring or summer to see it in its mothly glory.
We learned that it does well in very cold temperatures (more than 30 degrees below zero) and needs the colder temperatures for proper metamorphosis. For that reason, we will be placing our "friend" on the shaded north-facing front porch in the nice little home we've made him. We will await warm weather and the emergence of Mr. Moth.
When I was checking favorite blogs this morning, I stumbled upon a similar post by my friend, Andrea, who lives only about 15 minutes from us. It must be the year of the Crecopia Moth in our area!