There is a small but self-sustaining breeding population of cougars living in the Adirondacks and possibly most of upstate New York, but this will never be officially confirmed by the various government environmental agencies because then they would have to take real action to protect them. Cougars have everything they need there and there’s really no reason to believe they’re just walking 1800 miles and not breeding.
This is the case for a lot of other heavily forested places east of the Rockies as well.