John Henry Kagey, also spelled John Henrie Kagi (March 15, 1835 – October 17, 1859), was an American attorney, abolitionist and second in command to John Brown in Brown's failed raid on Harper's Ferry. He bore the title of "Secretary of War" in Brown's "provisional government." At age 24, Kagi was killed during the raid. He had also been active in fighting on the abolitionist side in 1856 in "Bleeding Kansas".
John Henry Kagi was born in Bristolville, Ohio, in 1835, the second child of blacksmith Abraham Neff Kagy (as spelled on his gravestone) and Anna Fansler, who were of Swiss descent. John Henry Kagi adopted the Swiss spelling of the family name.
Though largely self-taught, he was the best educated of Brown's raiders. Several of his letters to national newspapers survive, including those to the New York Tribune, the New York Evening Post, and the National Era. He was an able businessman, totally abstained from alcohol, and was agnostic.
In 1854-55 he taught school in Hawkinstown, Shenandoah County, Virginia near his father's birthplace, but he was compelled to leave due to his anti-slavery views. A relative, the Virginia historian Dr. John W. Wayland, wrote the most complete monograph on Kagi and his activities.
In 1855, Kagi traveled west and stayed at the cabin of his sister Barbara Kagy Mayhew and her husband Allen in Nebraska City. He helped them create a cave under their cabin to be used by fugitive slaves as a station of the Underground Railroad. Today the Mayhew Cabin is the only site in Nebraska recognized by the National Park Service as part of that escape system.