I expected someone would jump to give you more information but that didn't happen-at least not yet.
This information is taken from his pension file. John Cornish enlisted in the Continental Army at Portland in January of 1777 and served three years.Sorry but I can't copy and paste from where I read his file but it would be on Fold3.
According to an 1938 letter in his file there is no later information that what you have (nothing about when he or his wife died, when the pension was stopped, etc.).
For genealogy I would expect the DAR would lots of "stuff".