Seven Companies, "A" to "G," organized at Alton, Ill., and mustered in July 3, 1861. (Cos. "I," "H" and "K" were not mustered with Regiment and never served with it.) Companies "I," "H" and "K" were mustered at Alton at later dates and never served with the main body of the regiment. The original companies served as guards for supply trains and depots until mustered out on July 14, 1862. The remaining companies served independently.
The last company was mustered out on December 27, 1862.
The Regiment lost during service 17 Enlisted men killed and mortally wounded and 26 Enlisted men by disease. Total 43.
Colonel Thomas A. Marshall - mustered out July 14, 1862, with the main body of the regiment
Among their initial officers was future Washington philanthropist David P. Jenkins, who served as the regiment's first major
Attached to Dept. of Missouri. Moved to St. Charles, Mo., thence to Jefferson City, Mexico, Hannibal and Lexington, Mo. Skirmish at Georgetown, Mo., August (Co. "C"). Siege of Lexington, Mo., September 11-20. Surrendered September 20. Reorganizing at Benton Barracks, Mo., until June, 1862. Guard supply trains and depots at Rolla, Houston, West Plains, etc. Mustered out July 14, 1862. Company "H" organized at Alton, Ill., June 12, 1861. Company "I" organized at Alton, Ill., July 9, 1861. Company "K" organized at Alton, Ill., December 9, 1861. Companies "H" and "I" attached to Military District · of Cairo to February, 1862. 4th Brigade, 1st Division, Military District of Cairo, to March, 1862. Unattached, Army of Mississippi, to April, 1862. Cavalry Division, Army Mississippi, to June, 1862. District of Memphis, Tenn., to July, 1862.
Skirmishes at Charleston, near Bird's Point, August 19-20, 1861. Fish Lake August 20. Underwood's Farm, near Bird's Point, October 14. Action at Belmont, Mo., November 7. At Cairo, Ill., and Bird's Point, Mo., until March, 1862. Operations against New Market, Mo., March 1-14, and against Island No. 10, Mississippi River, March 15-April 8. Duty at New Madrid until June, and at Memphis, Tenn., until July. Mustered out July 15, 1862. Company "K" attached to Army of Southwest Missouri January to July, 1862. District of Eastern Arkansas, Dept. of Missouri, to October, 1862. Army of Southeast Missouri to December, 1862. Action at Warrensburg, Mo., March 28. Mustered out December 27, 1862.
Company A - McLean County
Company B - Gallatin County (Also Known as Gallatin County Cavalry)
Company C - Coles County
Company D - Knox County, Henry County, and Peoria County
Company E - Montgomery County
Company F - Adams County and Sangamon County
Company G - Warren County
Company H - Marion and Grundy counties (Also Known as Centralia Cavalry)
Company I - White County (Also Known as White County Cavalry)
Company K - Winnebago County (Also Known as Light Dragoons, Steele's Guards, Huntley's Cavalry Company)