It was April 1861 when word was received that Fort Sumter had been fired on in the first action of the Civil War. Soon, the U.S. Secretary of War was asking Gov. Samuel Kirkwood to raise a regiment as Iowa's contribution to the war effort.

Within 24 hours after the news of the president's call, more than a regiment had been met and more volunteers continued to step forward. Training camps were quickly established near many of the state's principal cities to equip the volunteers.

Iowa had no money to spend on an army so Kirkwood gave his personal bond, pledging all his property and earnings many times over so that the state's first soldiers might have shoes to wear, blankets to sleep on and bread to eat. Soon, supplies found their way to the camps and the recruits began building their own barracks and tables. They also made troughs for the horses that each cavalry volunteer brought to camp. Each horse owner received 40 cents a day for the use and risk of his animal.

Soon the Burlington Mounted Rangers — 125 men under the command of Capt. Chase — and the Hawkeye Rangers, raised in Clinton and Iowa City, joined the first twelve companies composed the First Iowa Cavalry when it was organized for United States service in 1861.

Company A was enrolled in Lee County and organized at Keokuk, Company B, the "Hawkeye Rangers," was also organized in the spring of 1861, chiefly from Clinton and Jackson counties. Company C was enrolled from the counties of Des Moines, Louisa, and Lee. Company D was enrolled from Warren and Madison counties. Company E was organized in Henry County. Company F was enrolled chiefly in the counties of Washington and Johnson. Company G, known as the "Hardin Rangers," was enrolled from the counties of Hardin, Dubuque, Black Hawk, Jones, and Delaware. Company H was enrolled in the counties of Monroe and Lucas, and organized at Albia. Company I went from Wapello and Keokuk counties, with a few from Hancock County, Ill. Company K, or "Union Rangers," was enrolled in Clayton, Allamakee, and Winneshiek counties.

By order of the Governor, these companies were directed to meet at Ottumwa, June 5, 1861, to organize into a regiment. No call had been made to Iowa for cavalry. By an act of Congress in July 1861, the number of companies constituting a cavalry regiment was raised from ten to twelve. This added to the First Cavalry Company L from Dubuque, Jackson, and Jones counties and Company M, the "The Black Plume Rangers," mostly from Clinton County. The Iowa Legislature tendered the regiment to the Secretary of War as an independent regiment.