On 23 June 1846, the 2nd Regiment, Ohio Volunteer Infantry was mustered into federal service at Camp Washington.

In April 1861, it was reorganized at Camp Jackson as the 3rd and 4th Regiments, Ohio Volunteer Infantry.

During 1876 and 1877, the companies were consolidated as a result of labor unrest and became the 5th, 6th and 14th Infantry Regiments of the Ohio National Guard.

After landing at New York City on 3 November, they were reviewed by President McKinley after being moved to Washington, D.C.[2] The regiment was mustered out at Columbus on 20 January 1899.

On 15 July, the regiment was called into federal service due to the United States entry into World War I.

[1] The 166th 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 Sherman, Ohio.

The regiment, or elements thereof, was called up to perform the following state duties: riot control during a coal miners’ strike at Cadiz and Zanesville, Ohio, 14 July 1922 – 8 August 1922; escort duties at the funeral of President Warren G. Harding in August 1923; tornado relief duties at Lorain and Sandusky, Ohio, 28 June–16 July 1924; guard duties at the crash site of the dirigible USS Shenandoah in September 1925; riot control during a coal miners’ strikes at St. Clairsville and Nelsonville, Ohio, 4 August 1927 – 10 June 1928; riot control during the Ohio State Penitentiary riot and fire, 21 April–3 June 1930; riot control during a coal miners’ strike at Cadiz, 16 April–20 July 1932; flood relief along the Ohio River, January–March 1937; riot control during a workers’ strike at the Mahoning Valley steel plants, 22 June–15 July 1937.

The regiment moved to New Orleans, Louisiana on 12 February, and the 1st Battalion was detached as part of Task Force 1291, serving as a garrison unit in Aruba and Curaçao in the Caribbean.

On 15 April 1943, it returned to Camp Shelby and became part of the Third Army, where the 2nd Battalion rejoined the regiment.

On 7 September, the regiment, less the 2nd Battalion (which was assigned to Camp Hood, Texas), was ordered to move to Fort Sill, Oklahoma.

On 22 January 1944, the 166th Infantry Regiment, less the 2nd and 3rd Battalion and Company D, was inactivated at Fort Sill.

[7][8][9] The 166th Infantry Regiment was reorganized on 11 November 1946 as part of the Ohio National Guard.