 The regiment served in this manner until the spring of 1864, when it was assembled to participate in Brigadier General Alfred Sully’s Northwestern Indian Expedition against the Sioux.The regiment rendezvoused at Paynesville, Minnesota, on May 24, 1864, where it received its regimental colors, was mounted on horses, and attached to the 2nd Brigade of the District of Iowa.The 8th marched through Dakota Territory, where it participated in the Battle of Killdeer Mountain in July, and at the Battle of the Badlands in August.