The 12th Illinois Cavalry Regiment was a volunteer cavalry regiment which served in the Union Army during the American Civil War. The 12th Cavalry was organized at Camp Butler in February 1862. It was part of the Army of the Potomac from September 1862 to November 1863; the Department of the Gulf from March 1864 to February 1865; and the Department of Texas from July 1865 to May 1866.