James Harrison Wilson (September 2, 1837 – February 23, 1925) was an American military officer, topographic engineer and a Major General in the Union Army during the American Civil War. He initially served as an aide to Major General George B. McClellan during the Maryland Campaign before joining Major General Ulysses S. Grant's army in the Western Theater, where he was promoted to brigadier general. In 1864, he transferred from engineering to the cavalry, where he displayed notable leadership in many engagements of the Overland Campaign. However, his attempt to destroy Lee’s supply lines failed when he was routed by a much smaller force of Confederate irregulars.

Returning to the Western Theater, Wilson became one of the few Union commanders to defeat Confederate cavalier Nathan Bedford Forrest in battle. He achieved this feat at the Battle of Franklin in November 1864 and again during his raid through Alabama and Georgia in March and April 1865. Wilson ended the war with his men capturing both Confederate President Jefferson Davis and Andersonville Prison commandant Henry Wirz in May 1865. At the time of his death in 1925, he was the fourth-to-last living Union Civil War general.

Wilson was born in Shawneetown, Illinois. He attended McKendree College for a year and graduated from the United States Military Academy in 1860, sixth in his class of 41, receiving a commission as a brevet second lieutenant in the Topographical Engineers. His initial assignment was assistant topographical engineer of the Department of Oregon at Fort Vancouver.

After the start of the Civil War, Wilson received promotions to second and first lieutenant and became the topographical engineer for the Port Royal Expeditionary Force, from September 1861 to March 1862. As the topographical engineer for the Department of the South, he took part in the Battle of Fort Pulaski at the mouth of the Savannah River and received a brevet promotion to major in the regular army for his service. He transferred to the Army of the Potomac in April 1862 and served as its topographic engineer, but also as an aide-de-camp to Maj. Gen. George B. McClellan. He served under McClellan during the Maryland Campaign and was present at the battles of South Mountain and Antietam.

Wilson was transferred to the Western Theater and joined Maj. Gen. Ulysses S. Grant's Army of the Tennessee as a lieutenant colonel and topographical engineer. During the Vicksburg Campaign, he was the inspector general of Grant's army. On October 30, 1863, he was promoted to brigadier general of volunteers. He continued on staff duty during the Battle of Chattanooga and was chief engineer of the force sent to relieve Knoxville under Maj. Gen. William T. Sherman.

In 1864, Wilson switched from engineering to the cavalry. On February 17, 1864, he was assigned as chief of the Cavalry Bureau in Washington, D.C. He was an excellent administrator and organizer, but his true talents turned out to be as a combat leader. Grant promoted him to brevet major general on May 6, 1864, and had him assigned to command a division of cavalry under Maj. Gen. Philip Sheridan, which he did with boldness and skill in numerous fights of the Overland Campaign and in the Valley Campaigns of 1864.

General Wilson's ill-fated joint adventure with General Brigadier General August V. Kautz was launched through General Grant's strategy of interdicting Robert E. Lee's supply lines to Petersburg, Virginia. If this could be done, Lee would be compelled to abandon Petersburg. General Wilson was ordered to conduct a cavalry raid that would destroy the tracks of the South Side and Richmond & Danville railroads, and to destroy the key R&D railroad bridge over the Staunton River. The raid began on June 22, 1864, with over 5,000 Cavalry troops and 16 pieces of artillery. During the first three days of their raid, Wilson's cavalry tore up 60 miles of track and burned two trains and several railroad stations. Confederate General W. H. F. "Rooney" Lee pursued the Union raid, but was ineffective. The audacious raid seemed to be wildly successful, though not uncontested, and the Staunton River Bridge loomed as the great objective. The railroad bridge was over a small but deep river, the Staunton. The Confederacy had sensed its strategic importance, putting a small fort there under Captain Benjamin Farinholt, and his 296 reserve troops. A valiant stand by local volunteers of old men and boys, with help from surrounding counties, gathered almost a force of nearly 1,000, which halted the 5,000 well-armed troops. Wilson’s cavalry fought the action dismounted. "Rooney" Lee's cavalry came up during the engagement's end, and routed Wilson's troops. There has been speculation that this damaged an otherwise brilliant career for Wilson.

However, just before Sheridan's decisive Battle of Cedar Creek in October 1864, Wilson was upgraded to brevet major general of volunteers and transferred back to the West to become chief of cavalry for the Military Division of the Mississippi under Sherman.