The 4th United States Volunteers, known as the 2d United States Volunteers until 1865, served in the Department of Virginia until 1865. They were transferred to the Department of Missouri with Lt. Col. Charles C. G. Thornton in command and 1st Lt. William H. Blyton, regimental quartermaster and acting assistant quartermaster at Fort Sully. The regiment served under Gen. Sully in the Northwestern Indian Expedition of 1865 and was mustered out of service in 1866.
From the description of United States. Army. Volunteer Regiment, 4th Records, 1863-1866. (Unknown). WorldCat record id: 702128309