In 1775, Rathbun received training with the Connecticut militia and, in May 1776, he was formally inducted.
On 19 September 19,1776, his father Benjamin and other residents of Hopkington, Connecticut, signed a declaration in support of the war of the “United Colonies” against Great Britain, pledging to assist the colonies. Rathbun fought with the elite forces of Captain Eliphilat Holmes as one of the Connecticut Minutemen, soldiers “on call”, interrupting their lives, dropping their plows and picking up their muskets at a “minute’s notice” to go to battle.
Following the war, Rathbun became a successful farmer in upstate New York. In 1808, he bought 300 acres in Howard, New York, and grew new strains of rye grain that he used to make whiskey in his distillery. He built a home that came to be called “the Castle,” which was large enough to raise his family and to hold town meetings. Until his death in 1838 in Howard, Steuben County, New York, he celebrated the Declaration of Independence’s guarantees of life, liberty, and property by growing his land holdings in ‘the old Castle district’ and leading the popular movement of rye whiskey artisan producers.