As I have said, many Bobcats are mistaken for Cougars, and tracks can easily be misidentified, as well as sightings by the untrained eye. Also, if there is an established cougar population, there would certainly be roadkills, which is unheard of near where I'm around. I do think rural, less populated regions of northern New England and New York are home to a small population of Cougars, with available space and plenty of prey items. In fact, one fellow volunteer at Beardsley said that her relative works on a train in upstate NY, and he sees legitimate Cougars, actually waiting for deer to run across the railroad. I do think however, that in coming years, more legitimate Cougar sightings will pop up in southern New England and other areas on the East Coast.
I think one of the biggest problems in determining if cougars exist in the eastern U.S. is that the Cougar is one of the most elusive predators out there, and can be a few yards from you, and you'd never notice. They're extremely hard to track.