He was graduated from Yale College in 1779. In 1781 he went to Groton to attend the wedding of his brother, Thomas Y. Seymour, to his cousin, Mary Ann Ledyard, and remained to visit his uncle, Colonel Ledyard. The British attack on Groton, led by the infamous Arnold, occurred at just this time, and young William Seymour led a company of hastily organized volunteers to the support of his uncle in defending Fort Griswold. He received a ball in the knee while repelling the assault, and afterwards seven wounds from the inhuman enemy, which crippled him for life. Miss Talcott received a tradition that he was the only American wounded at Fort Griswold who received attention from the British surgeon, and this was because he was recognized as belonging to a family of superior social position.
He became a merchant in Hartford, and lost his mind some years before his death.1)