Question

my grandfather's name was william taylor castleton, who was he?

Answer 1

What else do you know about William Taylor Castleton?  About whe was he born, married or died?  Where did he live?  The more information we have the better we can help with the right one.

Answer 2

Do you have his birth/death date and place or where he resided most of his life?

Could any of the following be him?

William Taylor Castleton

United States, World War II Draft Registration Cards, 1942
    
birth:    23 Dec 1895    
residence:    1942    Closter,​ Bergen,​ New Jersey
draft registration:    1942    Closter,​ Bergen,​ New Jersey
    
    
William T Castleton

United States Census, 1920
    
birth:    1896    New Jersey
residence:    1920    ,​ Bergen,​ New Jersey
    
    
William T. Castleton

New Jersey, Births and Christenings, 1660-1980
    
birth:    23 Dec 1895    Hgn.,​ Bergen,​ New Jersey
residence:    1895    New Jersey,​ United States
    
parents:    Edward A. Castleton,​ Bertha T. Taylor
    
William T Castleton

New Jersey, State Census, 1905
    
birth:    1896    
residence:    1905    ,​ Bergen,​ New Jersey,​ United States
    
    
William T Castleton

United States, World War I Draft Registration Cards, 1917-1918
    
birth:    23 Dec 1896    Closter,​ New Jersey,​ United States
draft registration:        Bergen County no 4,​ New Jersey,​ United Stat

https://familysearch.org/search/records/index#count=20&query=%2Bgivenname%3A%22william%20taylor%22~%20%2Bsurname%3Acastleton~