Henry Knox Thatcher (26 May 1806 – 5 April 1880) was a rear admiral in the United States Navy, who served during the American Civil War.

Appointed to the U.S. Military Academy at West Point in 1822, Thatcher was absent on sick leave for most of the first year and resigned in April 1823.

[1] Thatcher was promoted to captain in 1861,[5] and while commanding the large sloop of war Constellation in the Mediterranean, attained the rank of commodore[1] on 3 July 1862.

[2] Though put on the retired list on 26 May 1868[5] when he reached the age of 62, Thatcher served as Port Admiral at Portsmouth, New Hampshire, in 1869–1870.

[1] By right of his descent from his grandfather, Major General Henry Knox, Thatcher was a member of the Massachusetts Society of the Cincinnati.