In 1861–1862, Fish participated in the "Union Defense Committee of the State of New York", which co-operated with the City of New York in raising and equipping Union Army troops, and disbursed more than $1 million for the relief of New York volunteers and their families. The committee included chairman John A. Dix, William M. Evarts, William E. Dodge, A.T. Stewart, John Jacob Astor, and other New York men. Fish was appointed chairman of the committee after Dix joined the Union Army.