His father, within a few years after his birth, removed with his family to Cleveland, and became engaged in the wholesale grocery business in the firm of Hanna, Garretson & Company.
He served with that regiment at different posts during the years 1867—68, and in 1869 was appointed Signal Officer on the staff of Major General John Pope, commanding the Department of the Lakes at Detroit, Michigan.
In 1869, the Government began preparations for reducing the army to a peace basis, and inactivity and slow promotion being the result Garretson resigned from the service on January 1, 1870, with the permission of General W. T. Sherman, Commander-in-Chief, and with the full understanding that in case of need at any time his services would be tendered to the Government.
[2][3][4] Garretson was interested in the State militia, but owing to business reasons was compelled to decline any appointment until 1877, when at the time of threatened riots in Cleveland, he assisted Colonel W. H. Harris, late of the United States Army and a graduate of West Point, in organizing the First Cleveland Troop of Cavalry, of which Colonel Harris was captain and Garretson First Lieutenant.
In 1887 the troop became Troop A, Ohio Cavalry in the Ohio National Guard, Garretson remaining in command as captain until 1892, when business interests compelled him to resign and give up military matters, notwithstanding tempting offers of high rank in the State service had been repeatedly made to him.
[2][3] At the beginning of the Spanish–American War, he offered his services to President McKinley, and received his appointment as Brigadier General of U.S.
He was a trustee of the Lakeside Hospital, and took a strong interest in other charitable and benevolent institutions of Cleveland such as the Red Cross, the Fresh Air Camp, etc.