This moth was found clinging to our cedar wood sided garage on 5-19-2012 in Saint Paul Park, Minnesota. It was about 6 inches long, had a heart shaped back (between wing span), was brown and beige, very furry, and had an eye spot on its wings. I have never seen a moth of this size in the 25 years we’ve lived here.
Yes, it is a polyphemus moth. It looks like you have a newly emerged(from a cocoon) polyphemus moth. The silkmoths, Saturnid, are the largest of all moths and this is one of the most common. They overwinter in large silky light brown leaflike cocoons. So your weather has warmed up enough for them to emerge. The larvae become large green caterpillars.
It is certainly a beautiful specimen. So glad you got to see it. Unless you have bright lights on at night they do not usually show up.