Terry's Morris Island Division was redesignated the 1st Division, X Corps, and fought at the Battle of Proctor's Creek and in the Bermuda Hundred Campaign around Richmond. Once the Siege of Petersburg began, Terry continued to fight in the battles north of the James River, notably at the Battle of New Market Heights. Upon the death of X Corps commander David B. Birney in October, Terry briefly assumed command of the corps before it was dissolved. His leadership was never in question, but he had not achieved the same battlefield glory that many of his counterparts had won by this time in the war.
Terry's greatest achievement of the war came when he was placed in command of the Fort Fisher Expeditionary Corps. Benjamin Butler had previously failed in an expedition against Fort Fisher at the end of 1864. Terry had gained the confidence of General Ulysses S. Grant and was now in command of the ground forces in a second expedition against the fort. Unlike Butler, Terry worked well with the Navy under the command of David D. Porter. On January 13, 1865, Terry sent a division of United States Colored Troops to hold off Confederate forces under Braxton Bragg to the north of Fort Fisher. He sent his other division under Adelbert Ames against the northern part of the fort. After hand-to-hand fighting, the Union troops took control of the fort. For his part in the Battle of Fort Fisher, Terry was promoted to major general of volunteers and brigadier general in the regular army. Reinforcements arrived in February and John M. Schofield arrived to take overall command of the campaign against Wilmington, North Carolina. After the fall of Wilmington, the Fort Fisher Expeditionary Corps was renamed the X Corps, with Terry remaining in command, and participated in the final stages of the Carolinas Campaign. He is generally considered one of the most capable generals with no previous military training to emerge from the war.
Postbellum activities
After the war, Terry remained in the military. He helped to negotiate the Treaty of Fort Laramie, which ended Red Cloud's campaign against American troops in the region. Terry became a strong opponent of the Ku Klux Klan after being assigned as the last military governor of the Third Military District, based in Atlanta, where he served beginning on December 22, 1869. Terry was the commander of the U.S. Army column marching westward into the Montana Territory during what is now popularly known as the Centennial Campaign of 1876–77. Two other columns marched toward the same objective area. A column of troops under his command arrived shortly after the Battle of Little Bighorn and discovered the bodies of Custer's men. In October 1877, he went to Canada to negotiate with Sitting Bull. He was still in command in Montana during the Nez Perce War and sent reinforcements to intercept Chief Joseph. In 1878, Terry joined Maj. Gen. John Schofield on a presidential board asked to reexamine the conviction by court-martial of Fitz John Porter. The board found that Porter had been unfairly convicted of cowardice and disobedience. In 1881, as the Northern Pacific Railway's transcontinental rail line was building across Montana, the new town of Terry, Montana was named in his honor. In 1886, Terry was promoted to major general and was given command of the Military Division of the Missouri, headquartered in Chicago. He died four years later in New Haven, Connecticut, where he is buried in Grove Street Cemetery.
