Winthrop was born on December 22, 1863, in Paris, France, where his family was living during the U.S. Civil War.
[10] Through his father, he was a descendant of Wait Winthrop and Joseph Dudley (both Massachusetts Bay Colony leaders), and through his great-grandmother, Judith (née Stuyvesant) Winthrop, he was a direct descendant of Peter Stuyvesant, the Director-General of New Netherland,[11] and Robert Livingston the Elder, the 1st Lord of Livingston Manor.
[1] After his father's death, he inherited a one third portion of his estate, along with his brother and deceased sister's only child.
[20] He received his father's New York home and Newport cottage with his brother as tenants in common.
Winthrop's first summer home in Muttontown, New York (within the Town of Oyster Bay), now known as Nassau Hall, was designed by Delano & Aldrich around 1904.
[22] The 168 acre estate was purchased by Landsdell Christie, who sold the property to Nassau County in 1968.