Enlising as a private soldier, and continuing such from principle throughout the entire Rebellion, he survived its vicissitudes and dangers. After the war Underhill returned to New York and found employment in a law office. Following the war he applied and was reinstated into the Society of Friends in May 1868. He also became a member of the Ulysses S. Grant Post #327 of the Grand Army of the Republic. Underhill took an active interest in the Friends'; First Day School in 1866. He remained Superintendent for nearly twenty years. He also served as Clerk of Friends' Monthly Meeting. Late in life Silas A. Underhill married Frances Gertrude Lowerre, the daughter of Benjamin and Anna Lowerre, who already had a son and daughter. She had three children by way of her first husband Samuel Willis Rushmore. He lived at 119 Montague Street in Brooklyn, New York. Underhill studied law and practiced for several years before he became attached to the Supreme Court. Following the death of Silas Underhill, his wife Frances Gerturde Underhill appears to have moved to 335 Clinton Avenue in Brooklyn. Underhill was actively involved in efforts to erect a memorial for his Colonial era ancestor Captain John Underhill at the Underhill Burying Ground in Lattingtown, New York, and is named on the dedicatory plaque on the monument. He also served as Recording Secretary of the Underhill Society of America between 1892 and 1896. Silas Albertson Underhill died December 24, 1906, in the office of the Brooklyn Union Gas Company. His death was recounted as follows in one source: "Went into an office to pay a gas bill. Sat on a settee. His head partly fell. Asked if he was sick. Breathing heavy. In ten minutes he was dead." A Memorial Address on Silas Albertson Underhill was made at a meeting of the Underhill Society of America on February 16, 1907. The role of Silas Underhill in the dedication ceremony for the Captain John Underhill monument at the Underhill Burying Ground was recognized in a re-enactment that took place in 2008.