The original Regiment raised in 1689, thru various iterations and renamings finally became 1st Battalion in 1804 when 2nd Battalion was raised. When the regiment was associated with a number of Welsh counties after it became the South Wales Borderers in 1881, it gained those counties' militia and volunteer battalions. These were:
3rd Battalion - formerly the Royal South Wales Borderers Militia
4th Battalion - formerly the : disbanded in 1908.
The 1st Brecknockshire Rifle Volunteer Corps: renamed 1st Volunteer Battalion in 1885.
The 1st Monmouthshire Rifle Volunteer Corps: renamed 2nd Volunteer Battalion in 1885.
The 2nd Monmouthshire Rifle Volunteer Corps: renamed 3rd Volunteer Battalion in 1885.
The 3rd Monmoutshire Rifle Volunteer Corps: renamed 4th Volunteer Battalion in 1885.
In 1908 the Territorial Force was established and the volunteer battalions joined it. These became:
The Brecknockshire Battalion - formerly the 1st Volunteers
The three Monmouthshire battalions became The Monmouthshire Regiment, an entirely territorial infantry regiment, although part of the "corps" of the South Wales Borderers.
2nd Battalion, The Monmouthshire Regiment - formerly the 3rd Volunteer Battalion
3rd Battalion, The Monmouthshire Regiment - formerly the 4th Volunteer Battalion
The 5th Volunteer Battalion ceased to be part of the South Wales Borderers, and was transferred to the Royal Welsh Fusiliers to form part of the 7th Battalion of that regiment.
First World War
The regiment, along with its Territorial units, raised nineteen battalions: all these battalions were either disbanded during the war or in the immediate aftermath of it.
2/1st Brecknockshire Battalion - formed in September 1914 at Brecon. The Battalion joined the 68th Division in 1915. It was absorbed by the 2/7th Royal Welsh Fusiliers in November 1916.
3/1st Brecknockshire Battalion - formed in April 1915 at Brecon. The Battalion became the 1st Battalion in April 1916. The following year, in August, it amalgamated with the 1st Battalion, Monmouthshires.
4th Battalion - formed in August 1914 at Brecon. The Battalion joined the 13th Division and saw service in Gallipoli and Mesopotamaia.
10th Battalion - formed in December 1914 at Ebbw Vale. It joined the 43rd Division and saw service on the Western Front.
11th Battalion - formed in December 1914 at Brecon. Joined the 43rd Division and saw service on the Western Front. It was disbanded in February 1918 in France.
12th Battalion - formed in March 1915 as a Bantam battalion of the Welsh Bantam Brigade. The battalion joined the 40th Division in September and saw service on the Western Front, where it was disbanded in February 1918.
13th Battalion - formed in July 1915 at Abertillery, Monmouthshire as a local reserve battalion for the 10th, 11th and 12th Battalions. It became the 59th Battalion, 13th Reserve Brigade in September 1916.
2/1st Battalion, The Monmouthshire Regiment - formed in September 1914 at Newport. Joined the 68th Division and remained in the UK for the duration of the war; it was disbanded in March 1918.
2/2nd Battalion, The Monmouthshire Regiment - formed in September 1914 at Pontypool. It joined the 68th Division and remained in the UK where it was disbanded in April 1919.
2/3rd Battalion, The Monmouthshire Regiment - formed in September 1914 at Abergavenny. Joined the 68th Division and remained in the UK until it was disbanded in August 1917.
3/1st Battalion, The Monmouthshire Regiment - formed in February 1915. In April 1916 it became a Reserve Battalion. In July 1917 it absorbed the 3/2nd and 3/3rd, Monmouthshires, all of which had identical histories to the 3/1st. It remained in the UK for the duration of the war.
4th Battalion, The Monmouthshire Regiment - formed in 1916 as the 48th Provisional Battalion from home service members of the Monmouthshire and Herefordshire Regiments; transferred to the regiment in January 1917, becoming its 4th Battalion. It remained in the UK for the duration of the war.
Inter-War
3rd Brecknockshire and Monmouthshire Battalion - formed in 1922 when the Brecknockshire Battalion was absorbed by the 3rd Battalion, Monmouthshires. The battalion transferred to the Royal Artillery in 1947.
The regiment, along with its Territorial units, raised 5 battalions during the war, all of which were either disbanded during the war or in its immediate aftermath.
5th Battalion - formed in 1939.
6th Battalion - formed in July 1940 at Brecon. The Battalion transferred to the Royal Armoured Corps as the 158th Regiment in April 1942. It re-roled as an infantry regiment in March 1943. It saw service in the Far East.
30th Battalion - formed in 1941.
The Brecknockshire Battalion - reformed in 1939 and transferred to the Royal Artillery in 1947.
4th Battalion, The Monmouthshire Regiment - formed in June 1939. It was redesignated as 1st Battalion South Wales Borderers in December 1942. The original 1st Battalion SWB had been disbanded in August 1942 in Cyprus, most of the unit having been taken prisoner or becoming casualties in North Africa.
Post-War
Welsh Volunteers - formed in 1967 from the Territorial battalions of the Welsh Brigade. The 2nd Battalion, The Monmouthshire Regiment lineage was maintained by B Company.
