This regiment was composed of companies raised during the summer and fall of 1861, principally from the counties of Hardin, Allamakee, Fayette, Linn, Black Hawk, Delaware, Winneshiek, Dubuque and Jackson. The last company was sworn in on the 25th of November. J. J. Woods was commissioned colonel; J. P. Coulter, lieutenant-colonel, and S. D. Brodtbeck, major. It was moved to Benton Barracks near St. Louis, where, during the month of December it lost seventy-five of its number from sickness. In February it joined Grant's army, where it participated in the capture of General Buckner's army and Fort Donelson. It was in the battle of Shiloh and fought bravely all through that terrible Sunday, and had to surrender to overwhelming numbers just before sundown. Colonel Woods was severely wounded and the loss in battle by the regiment before surrender was very heavy. The prisoners were sent south. In May about half of them were paroled and sent to Benton Barracks, the rest suffered the hardships of rebel prisons until the 20th of November, when they were paroled. In April, 1863, the regiment was reorganized and sent to Rolla, Mo. Lieutenant-Colonel Coulter had resigned and Major Edgington was promoted to his place and Capt J. H. Stibbs was appointed major. The Twelfth was now placed in the Third Brigade of the third division of the Fifteenth Army Corps, and joined in the Vicksburg campaign. After that campaign the regiment now commanded by Major Stibbs was on duty at various points in the south and participated in the Meridian expedition under Sherman. In January, 1864, most of the men re-enlisted and the Twelfth became a veteran regiment, and they were granted furloughs to visit their homes.
In May the regiment was sent to Memphis, and in July fought bravely in the vicinity of Tupelo in repelling an attack upon the army trains, losing heavily in killed and wounded.
In June it made a brilliant defense of a post at White River, beating off General Marmaduke's attack with heavy loss.
In October the regiment was with Gen. A. J. Smith's army in pursuit of Price, in Missouri, and endured hard marching and hard fare.
In December the Twelfth was with General Thomas in the siege of Nashville and fought with its usual valor, and joined in the pursuit of Hood's army. It was in the Mobile expedition and participated in the siege and capture of that city, and remained in the service until 1866.
SOURCE, Benjamin F. Gue, Biographies And Portraits Of The Progressive Men Of Iowa, Volume 1, p. 98-9