Hi. I don't know if this thread is still active, but I think his grave is in the woods on a piece of property I bought last year! It reads William N Deyo and has his year of death listed as 1911. We are indeed up Augustine road, off of Manorville in West Saugerties. There are a few graves in the cemetery and you can make out the names of at least two of the family members (I think the other name might be Linda?).
I'd be happy to take photos of the graves and email them to you, or help you out in any way I can. We were excited to learn of the cemetery when we bought the property and fully intend to eventually clean it up and show it the respect we feel it deserves! Take care,