Commander: Major Samuel J. Wheeler.
Though not designated Partisan Rangers it fought irregularly. It was organized on 3 May 1863 and Major Wheeler was given authority to raise a regiment of Partisan Rangers and began raising it in October 1862. He managed only to raise four companies and the unit was disbanded and instead he was put in charge of this battalion from April 1863. Major Wheeler was promoted to Lt. Colonel but resigned in August 1863. The companies of the battalion were placed in other units. In March-April 1864 the battalion was recreated but only for a short time and the companies were transferred to other units.
In July the 12th ceased to exist. It took part in campaigns in the state only and was at times assigned to picket duty.