You can (and should) report the finding to the PA chapter of the American Chestnut Foundation. 

https://patacf.org/

There is a significant amount of research and work happening at PSU regarding this species, to the point that their hybridization efforts with the Chinese chestnut are at a point where DNA testing is usually required to determine American vs hybridized chestnuts. 

We ordered some trees through the Ten Million trees initiative with the Chesapeake Bay Foundation a few years ago, but just prior to delivery we were told they tested as hybrids despite advertising as American. We planted them anyway. I hope to one day plant American chestnuts on our farm for my kids, but that's still a few years away from being commercially available (last I checked).

Finding chestnuts in the wild, even hybrid, is a rare and awesome experience! Anyone interested, especially local to PA should sign up for the PA chapter newsletter to follow their work.  

 I've seen Chinese Chestnut before, there's actually a lot of them where I run, but I don't believe I've seen a hybrid before and this could be one, but due to its size and leaf characteristics, I'm fairly confident it's American.

This is a good idea! Maybe I will report it. I had a friend years ago that found a much larger one and did report it. PSU came down and tested it and did determine it was pure American, growing from an old root system!