Myles Walter Keogh, KSG (March 25, 1840 – June 25, 1876) was an Irish soldier. Serving the armies of the Papal States during a rebellion in Italy, he was recruited into the Union Army during the American Civil War, serving as a cavalry officer, particularly under Brig. Gen. John Buford during the Gettysburg Campaign and the three-day battle that ensued.

Myles Keogh was born in Orchard House, Leighlinbridge, County Carlow. He attended the National School in Leighlinbridge where he was enrolled under the spelling 'Miles Kehoe'.

 By 1860, a twenty year old Myles Keogh had volunteered, along with over one thousand of his countrymen, to rally to the defence of Pope Pius IX following a call to arms by the Catholic clergy in Ireland. By August 1860, Keogh was appointed second lieutenant of his unit in the Battalion of St. Patrick. He was posted at Ancona, a central port city of Italy. The Papal forces were defeated in September in the Battle of Castelfidardo, and Ancona was surrounded. The soldiers, although having admirable defence, were forced to surrender and Keogh was imprisoned at Genoa. After his quick release by exchange, Keogh went to Rome and was invited to wear the spirited green uniforms of the Company of St. Patrick. During his service, the Holy See awarded him the  Pro Petri Sede Medal and also the Cross of the Order of St. Gregory – Ordine di San Gregorio.

Now that the fighting was over and duties of the Vatican Guard were more mundane, Keogh saw little purpose in remaining at Rome. With civil war raging in America, Secretary of State William H. Seward began seeking experienced European officers to serve the Union, and called upon a number of prominent clerics to assist in his endeavour. John Hughes, Archbishop of New York, travelled to Italy to recruit veterans of the Papal War, and met with Keogh and his comrades. Thus in March 1862 Keogh resigned his commission in the Company of Saint Patrick, and with his senior officer – 30-year-old Daniel J. Keily of Waterford – returned briefly to Ireland, then boarded the steamer "Kangaroo" bound from Liverpool to New York, where the vessel arrived April 2.

Through Secretary Seward's intervention, the three were given Captains' rank and on April 15 assigned to the staff of Irish-born Brigadier General James Shields, whose forces were about to confront the Confederate army of Stonewall Jackson.

After the war, Keogh remained in the regular United States Army as commander of Company I in the 7th Cavalry Regiment under George Armstrong Custer during the Indian Wars, until he was killed along with Custer and all of his men at the Battle of the Little Bighorn in 1876.

Keogh's remains were interred in Fort Hill Cemetery  in Auburn, New York on October 26, 1877, an occasion marked by city-wide official mourning and an impressive military procession to the cemetery.The prominent Throop-Martin family, with whom Keogh had become friendly after his comrade General A.J. Alexander married Evelina Martin, was responsible for his burial in their Fort Hill plot and the design of his monument. At the base of decorative, white obelisk there is an inscription taken from the poem, The Song of the Camp by Bayard Taylor:

"Sleep soldier still in honored rest, Your truth and valor wearing; The bravest are the tenderest, The loving are the daring."

The marble cross atop his grave was added later at the request of his sister in Ireland.

Fort Keogh, in southeastern Montana, was named after Keogh. The fort was first commanded by Nelson A. Miles. The 55,000 acre fort is today an agricultural experiment station. Miles City, Montana is located two miles from the old fort.