Guy:
The Sooy family is tough. Writing in the late 1870s, Leah Blackman stated,
I have been unable to learn much about the geneology [sic] of the Sooy family. They do not properly belong to Egg Harbor township. The first generations of the Sooy family made extensive locations of land in Washington township. The Sooys of Atlantic county are the descendants of Yose Sooy, and it is probable they are the descendants of Luke Sooy.
According to the section in Blackman’s work on the Sooy family, Yose had at least three sons: Nicholas, Joseph and Luke. She notes Yose probably had other sons and daughters, but their names are unrecorded. Blackman does report that Nicholas had a son, William and Nicholas Jr. had a son, William. It appears that Nicholas Sr.’s son, William carried the qualifier “Senior” on the end of his name and, likewise, Nicholas Jr.’s son, William, carried the qualifier “Junior.”
While Blackman does not provide dates or even years in her genealogical work, I would guess the stone you found stems from William Jr., based on an interpolation of generations and when surveyors first began to set stones as property markers.
Best regards,
Jerseyman