You're probably right Nigel.
My long time neighbor Harry, bless his soul, always called them white tails, but looking up white tails their range doesn't come close to Pennsylvania: White-tailed Hawk Sightings Map Now the Cooper's Does: Cooper's Hawk Range Map

Looking to the right on this page: Cooper's Hawk shows an immature Cooper's, image is clickable. Still, it'd be interesting to hear what your friends have to say.