Constituted 22 May 1846 and organized in June 1846 as 1st Kentucky Cavalry Regiment and 2nd Kentucky Volunteer Infantry from volunteers of the enrolled militia, principally from counties near Lexington, KY.

Mustered into Federal Service for the Mexican War 9 June 1846, in Louisville. Mustered out of Federal service 7 June 1847.

Reorganized 15 June 1860 in the Kentucky State Guard as the Lexington Battalion, to include the Lexington Rifles which had been organized in 1857 by Captain John Hunt Morgan.

Expanded 6 November 1860 to form the Lexington Battalion and the Kentucky River Battalion.  These two battalions broke up in 1861 and reorganized as follows:

Elements with Union sympathy reorganized April-June 1861 primarily as the 1st and 2nd Kentucky Volunteer Infantry Regiments and mustered into Federal service 4 and 13 June 1861, respectively, at Camp Clay, Ohio; mustered out of Federal service 18 and 19 June 1864, respectively, at Covington, Kentucky.

Elements with Confederate sympathy (less Lexington Rifles) reorganized in July 1861 as elements of the 1st Kentucky Brigade (The Orphan Brigade) and mustered into Confederate service at Camp Boone, Tennessee. Surrendered 4 may at Washington, Georgia.

Lexington Rifles withdrew from the state guard 20 September 1861 and moved secretly to Bowling Green and reorganized as a separate company of cavalry, Confederate States Army. Consolidated in October 1861 with two other cavalry companies and reorganized and redesignated as Morgan's Squadron, Kentucky Cavalry.  Expanded, reorganized and redesignated in June 1862 as the 2nd Kentucky Cavalry Regiment (Morgan's Men). Surrendered near Woodstock, Georgia 8 May 1865 and paroled.

Reorganized in 1884 as an organic battalion of the 2nd Regiment of the Infantry Kentucky State Guard.

In Federal Service for World War I June 1916 – February 1917 as 2^nd Infantry, Kentucky National Guard and 1917 – 1919 as 149^th Infantry, as an element of the 38^th Division.

Withdrew from parent regiment 30 July 1921 and consolidated with 138^th Machine Gun Battalion.

Reorganized as 53^rd and 54^th Machine Gun Squadron, Cavalry, 138^th Machine Gun Battalion. Reorganized 1 April 1929 as 123^rd Cavalry.

Redesignated 1 November 1940 as 103^rd and 106^th Separate Battalions, Coastal Artillery (Anti-Aircraft) and entered Federal Service for World War II 6 January 1941.

Redesignated 29 January 1947 as 623^rd Artillery Battalion. Ordered to active duty for Korean War 23 January 1951. Released from active service 18 March 1955.

Reorganized and redesignated 1 October 1959 as 4^th Howitzer Battalion, 138^th Field Artillery.

Reorganized and redesignated 1 May 1969 as 623^rd Artillery, a parent regiment under the combined arms regimental system to consist of the 1^st Battalion.

Ordered to active duty for Operations Desert Shield/Storm 9 December 1990 as a subordinate of 196^th Field Artillery Brigade. Deactivated 21 May 1991.