Hello. While I wish you the best, it has been my experience that finding a grave site may be rather difficult.
This is one of those nowadays things that we from this time frame think that the info should be readily available. It is very probable that the man was buried and everyone knew where and then everyone died off. He may have even had a tree planted by his grave or a big rock put on it at the time.
That is what is called the voice of experience.
I would suggest you nail down a date of death and check to find out where the family was buring their dead at the time. Read the census if you have not to see when was the last time he was listed as living. If you happen to find a family Bible that says he died at a certain time, you are very fortunate. If it was after 1900, it has been my experience that you have a greater chance of finding an obit on this person.
Back at the time this man possibly died, I can almost assure you that keeping the living alive was the most important thing going. Monuments as we know them and obits as we know them were simply not done by anyone except the rich who had money to spend on such. I hope that everything I have said turns out to be wrong, but you just never know until you seriously search.
Good luck with your search.