The 9th Wisconsin Infantry was organized as a German Regiment at Camp Sigel, Milwaukee, and mustered into the service of the US 26 October with manpower strength of 870. It left the state on 22 January 1862, and traveled to Fort Leavenworth, Kansas, arriving on 29 January.

The 9th first took part in the "Southwestern Expedition" into Kansas, Missouri and the Indian Territory. It routed two Confederate camps at Cowskin Prairie, Missouri as well as a large camp of Confederate Indians en route, and took part in an engagement at Newtonia, Missouri against a superior force pending the arrival of the main body.

It was engaged at Cane Hill, Jenkins' Ferry, Terre Noir Creek, Prairie Grove, and Poison Springs, Arkansas. On the 2 March the 9th, together with other portions of the Army in that territory, participated in various movements on the frontier until 30 September, when the 9th was engaged in the battle at Newtonia, Missouri. On 27 November the Division of which the 9th was a part, advanced into Arkansas and was a part of the Union force present at the battle of Prairie Grove, 7 December 1862.

The 9th participated in numerous expeditions during 1863 and 1864 in Arkansas, including the Camden Expedition 23 March to 3 May 1864 under General Steele, taking part in the battle of Jenkins Ferry, Arkansas 30 April 1864, and a large number of minor engagements. The service of the 9th was chiefly rendered in Arkansas and Missouri, which included skirmishes, guarding of railways and frequent long and arduous marches and expeditions in various directions.

The foregoing does not do this Regiment full justice. Its membership included a large number of veterans of the German army. It was a well-disciplined body, organized with General Fremont's promise that it should be joined to General Sigel's command, and it expected to be sent to the front at once.

Instead it was sent on arduous, disheartening campaigns among scattered bands of guerrillas and Indians, suffering great privations and being in small engagements. Through all, in the face of keen disappointment, it maintained the traditions of the army of the former Fatherland, performed its duty admirably, and won praise for its gallantry.

The 9th was mustered out January 30, 1866, and was disbanded at Madison, WI, February 14, 1866

Its total enrollment was 1,422. Losses by death 175, desertion 25, transfer 7, discharge 191.