Mustered in at Dubuque, September 24, 1861, it left the State on the 26th, 1,007 strong, and proceeded to Benton Barracks, St. Louis. Four months of active service were passed in Missouri, and then it joined Curtis's Army of the Southwest, having been assigned to Vandever's Brigade, Carr's Division. It fought at Pea Ridge, withstanding a severe attack and sustaining the heaviest loss of any regiment on that field, its casualties amounting to 38 killed, 176 wounded, and 4 missing,--a total of 218 out of 560 engaged. The regiment arrived at Helena, Ark., in July, 1862, remaining there five months and then embarking in December, 1862, for Chickasaw Bayou, where it was under fire. The spring of 1863 was passed in camp at Young's Point, on the Mississippi, where its ranks were sadly depleted by disease. The Ninth was actively engaged at the Siege of Vicksburg, losing there 121 killed or wounded. In the assault on Vicksburg, May 19th, it lost 4 killed and 12 wounded; in the assault of May 22d, it lost 18 killed and 60 wounded. In January, 1864, 287 men reënlisted, received the customary furlough of one month, and returned accompanied by 125 recruits. The Ninth served during the Atlanta campaign in Osterhaus's (1st) Division, Fifteenth Corps, losing in that campaign,-- from May 1st to September 1st,-- 14 killed, 70 wounded, and 6 missing. While on the March to the Sea, it was in Stone's Iowa Brigade, C. R. Woods's (1st) Division, Fifteenth Corps.