It was reorganized on 1 January 1864 as the 4th Iowa Veteran Infantry Regiment, and mustered out of federal service 24 July 1865 at Louisville, Kentucky.

It was reorganized on 26 March 1900 in the Iowa National Guard as the 51st Infantry Regiment with its headquarters at Des Moines.

The 168th Infantry arrived at the port of New York on 25 April 1919 on the troopship USS Leviathan and was demobilized on 17 May 1919 at Camp Dodge.

The entire regiment, or elements thereof, was called up to perform the following state duties: tornado relief work at Neola and Persia, Iowa, 7–8 June 1925; riot control during the “Cow War” at Cedar County/Burlington, Iowa, 21 September–25 November 1931; the 1st and 3rd Battalions performed martial law in Plymouth and Crawford Counties, respectively, during the Farmers' Holiday Association disturbances, 28 April–17 May 1933; the 1st Battalion performed martial law at Newton, Iowa, during the labor troubles at the Maytag washing machine plant, 19 July–6 August 1938.

The regiment was inducted into federal service at home stations on 10 February 1941 and moved to Camp Claiborne, Louisiana, where it arrived on 3 March 1941.

The 168th Infantry returned to the United States via the Hampton Roads Port of Embarkation, Virginia on 3 November 1945 and was inactivated on the same date at Camp Patrick Henry.

The battalion was ordered again into active federal service on 31 July 2010 at home stations to deploy to Afghanistan in support of Operation Enduring Freedom (OEF).

[citation needed] Upon deployment into Afghanistan, 1st Battalion, 168th Infantry became Task Force 1-168 and assumed responsibility for the Afghan Province of Paktya.