Recruited among the German population of the state, the Ninth Wisconsin Volunteer Infantry mustered in at Camp Sigel, Milwaukee, on October 26, 1861. After reporting to Fort Leavenworth, Kansas in early January 1862, the Ninth joined the "Southwestern Expedition" into Kansas and Oklahoma. Among the other forces amassed for the expedition were two Indian infantry regiments. The leader of the expedition, Colonel William Wier, inflicted needless hardships on the men, marching them endlessly without supplies, foraging into Indian Country, and leaving his communications in possession of the enemy. At the request of his subordinate officers, Wier was later arrested and removed from the post.
Moved to the reorganized "Army of the Frontier," the Ninth immediately saw action at Newtonia, Missouri in late September 1862. Four companies of the Ninth unknowingly charged a superior Rebel force concealed behind a stone fence. Despite their valiant effort, the enemy turned their flanks, surrounding them, and later overtaking the Wisconsin contingent in the woods. In all, 28 men died and the Confederates took 167 prisoners.
In 1864, the Ninth occupied the post of rear guard at the Union Army's crossing at Jenkins' Ferry. Against nearly 20,000 of General Kirby Smith's Rebels, the Ninth and the rest of the First Brigade gallantly held the line, forgetting, as General Friedrich Salomon said, "...they were tired, that they were hungry, [and] only remembered that they were ordered to hold their ground." After the initial attack, the crossing proceeded without further incident. The Ninth Wisconsin later fell back to Little Rock, where they remained stationed for the duration of the war.