Can't say I've ever seen one but it appears we have one near us in NW St. Charles County. Saw it last week from about 75 -100 yards but it was flying and landed in a tree. With no foliage on the trees and the turns it made as it lit in the tree, I got a relatively good look at it. No question it is a hawk of some sort and no question is was white as snow. Appeared to be about the size of a Red-Tailed hawk.

Keeping my eyes peeled for it now. Hoping to get a better look and a pic.