He was killed by his brother Baker with an oar while in a canoe on the Piscataqua River. The brother claimed he was acting in self-defense and was found not guilty by a jury.

SOURCES AND MORE:

https://bangordailynews.com/2013/10/27/living/did-stephen-kings-ancestor-suffer-death-by-canoe-oar/

https://nutfieldgenealogy.blogspot.com/2010/02/baker-nason-murdered-his-brother-1691.html