Thomas Casimer Devin (December 10, 1822 – April 4, 1878) was a United States Army officer and general.

Gen. George Stoneman's raid and he successfully led three Union Corps on the stealthy flanking march that preceded the battle.

As the Confederate attacks began, Devin's brigade was screening the northwest and northern road approaches to Gettysburg, and successfully delayed the arrival of Jubal A.

On November 19, 1864, President Abraham Lincoln appointed Devin brigadier general of volunteers for his part in the Battle of Cedar Creek, to rank from October 19, 1864.

[3] President Johnson also appointed Devin brevet colonel in the regular army for Fisher's Hill, to rank from March 2, 1867.

Initially serving with part of the regiment in New Mexico, Devin assumed command of the Subdistrict of Prescott in Arizona in late 1867.

[6] Devin died of stomach cancer and exposure at his home in New York City, on sick leave from active duty, as Colonel of the 3rd U.S. Cavalry.

On June 30, 1878, the United States Army established a temporary camp in southeastern Montana Territory during the building of the Fort Keogh-Deadwood Telegraph Line.

Devin was portrayed by David Carpenter in the 1993 film Gettysburg, based on Michael Shaara's novel, The Killer Angels.