The 45th Kentucky Mounted Infantry Regiment was organized at large and mustered in on October 10, 1863, under the command of Colonel John Mason Brown.

The regiment was attached to District of North Central Kentucky, 1st Division, XXIII Corps, Department of the Ohio, to January 1864.

District of Southwest Kentucky, 1st Division, XXIII Corps, to April 1864.

First organized as a battalion for service in the eastern counties of Kentucky and on the Virginia border, and so served until October 1863.

Moved to Flemmingsburg March 1864; thence to Irvine, Ky., and operated south of that point until July.

Operations against guerrillas in Owen and Trimble Counties July and August.