On his mother's side he traced his ancestry to Robert Day, who emigrated from Ipswich, England in 1634, settled in Cambridge, Massachusetts, and in a few years removed to Connecticut and helped to found Hartford.

[1] Thomas Thacher prepared for college at the Hopkins Grammar School before attending Yale University.

His first professional association was with Ashbel Green, then one of the leaders of the New York Bar, with whom he collaborated in the preparation of Brice's Ultra Vires, which became a standard American work on corporation law.

During his forty-five years of active practice at the bar, the economic life of the country was undergoing a great transformation in the rapid development of production on a large scale.

[3] Mr. Thacher was married December 1, 1880, in New York City, to Sarah McCullough, daughter of Ashbel and Louise B.

(Walker) Green, of Tenafly, who survived him with a son, Thomas Day Thacher (Yale BA 1904), and three daughters.

[1] Thomas Thacher died at his daughter Sarah's home in Watch Hill, Rhode Island on July 30, 1919.