Dear Mr. Astles,
Thank you for posting your request on History Hub!
As parental names are often on death certificates, we suggest that you contact the New York State Archives to request a search of their death index, then with the certificate number and the exact date of his death, contact the clerk of the town/village where the death occured or the New York State Department of Health to obtain the death certificate of John Kelley Dean.
We hope this is helpful. Best of luck with your family research!