University of Michigan.
His family moved to Illinois in 1854. He joined the army as a civilian foragemaster and served on the staff of Albert Sidney Johnston during the Utah War of 1857–1858. He also worked as a buffalo hunter and scout in the Colorado Territory.
Being promoted to captain on December 25, 1861, he was made Assistant Chief Quartermaster of the IV Corps, and in early 1863, he served as aide-de-camp to Brigade
General Alfred Pleasonton through the Battle of Chancellorsville and early stages of the Gettysburg Campaign. On June 29, 1863, just two days before the Battle of Gettysburg, he was promoted to brigadier general of volunteers by Pleasonton, although this appointment was never confirmed by the United States Senate.
He was given command of 1st Brigade, 3rd Division, Cavalry Corps, Army of the Potomac. Death at Gettysburg
After the collapse of Pickett"s Charge and the defeat of Major
General J.E.B. Stuart"s Confederate cavalry on July 3, the third day of the Battle of Gettysburg, Brigade
General Hugh Judson Kilpatrick, commanding the 3rd Division, ordered Farnsworth to make a charge with his brigade against Confederate positions south of the Devil"s Den area of the battlefield, below Little Round Top. Farnsworth initially balked, arguing there was no hope of success, and only agreed to it when Kilpatrick allegedly accused him of cowardice.
Farnsworth made the charge, against elements of John B. Hood"s division, under Evander M. Law (Hood having been wounded the previous day).
Farnsworth rode with the second battalion of the 1st Vermont Cavalry, alongside Major William Wells. The charge was repulsed with heavy losses, and Farnsworth himself was shot five times in the chest. An account by Confederate Colonel William C. Oates claimed that Farnsworth was surrounded by Confederate soldiers and committed suicide to avoid capture, but this has been disputed by other witnesses and discounted by most historians.
Kilpatrick received much criticism for ordering the charge, but no official action was taken against him.
Farnsworth is buried in Rockton Cemetery, Rockton, Illinois. Battery Farnsworth, a coastal defense built between 1897 and 1899 near Fort Constitution at New Castle, New Hampshire, was named in his honor.
A member of the Chi Psi Fraternity, Farnsworth was expelled from the University of Michigan following a drinking party in which a classmate died after being thrown from a window.