The 81st Ohio Infantry was originally organized as "Morton's Independent Rifle Regiment" and mustered in for three years service under the command of Colonel Thomas Morton.

The regiment was attached to Department of Missouri, to March 1862.

2nd Brigade, 2nd Division, District of Corinth, Mississippi, to September 1862.

1st Brigade, 2nd Division, District of Corinth, Mississippi, to November 1862.

2nd Brigade, District of Corinth, Mississippi, XIII Corps, Department of the Tennessee, to December 1862.

2nd Brigade, District of Corinth, XVII Corps, to January 1863.

2nd Brigade, District of Corinth, XVI Corps, to March 1863.

The 81st Ohio Infantry mustered out of service at Louisville, Kentucky, on July 13, 1865.

Expedition to Fulton, Calloway County, Mo., November 1861.

Expedition after guerrillas in northern Missouri December 20, 1861, to January 4, 1862.

Moved to St. Louis, Mo., then to Pittsburg Landing, Tenn., March 1–15, 1862.

Moved to Pocahontas June 3, and duty there until October 29.

Snake Creek Gap and Sugar Valley, near Resaca, May 9.

Operations on line of Pumpkin Vine Creek and battles about Dallas, New Hope Church, and Allatoona Hills May 25-June 5.

Operations about Marietta and against Kennesaw Mountain June 10-July 2.

Reconnaissance from Rome on Cave Springs Road and skirmishes October 12–13.