Where precisely is the "high point" separating the St. Lawrence, Susquehanna, and Mississippi watersheds?

Answer 1

It may be in Potter County, Pennsylvania, from which tributaries drain into all three watersheds.
One of five North American Triple Points is located in Pennsylvania. An unnamed hill in Potter County is the intersection of Eastern Continental Divide and the St. Lawrence Seaway Divide.
http://geology.com/state-map/pennsylvania.shtml (maps of Pennsylvania)
http://nationalatlas.gov/articles/geology/a_continentalDiv.html (Map of North American watersheds)
http://www.dep.state.pa.us/river/basininfo.htm