The regiment was formed on the creation of the Territorial Force in April 1908 and placed under orders of the London Mounted Brigade. It was based at Henry Street in St John’s Wood. Its Volunteer Force predecessor had fought in the Boer War as the 3rd County of London Imperial Yeomanry (Sharpshooters).
1/3rd County of London Yeomanry
- August 1914 : moved with the brigade to Hounslow and then to join 2nd Mounted Division at Streatley.
- November 1914 : moved with brigade to North Walsham.
- April 1915 : moved to Egypt.
- August 1915 : dismounted and moved to Gallipoli.
- December 1915 : returned to Egypt and remounted.
- January 1916 : Division broken up; brigade moved to Suez Canal Defences and renamed 8th Mounted Brigade.
- November 1916 : moved to Salonika.
- June 1917 : returned to Egypt; brigade under orders of Yeomanry Mounted Division (21 July).
- 24 April 1918 : division renamed 1st Mounted Division.
- 22 July 1918: brigade renamed 11th Cavalry Brigade.
- “E” Battalion of the Machine Gun Corps was formed by the amalgamation of the 1/1st City of London Yeomanry and the 1/3rd County of London Yeomanry, in Egypt on 7 April 1918. Moved to Western Front by early June 1918. Redesignated 103rd Bn MGC on 19 August 1918.
2/3rd County of London Yeomanry
- Formed in September 1914 as a “second line” (training, draft-supplying reserve) for the 1/1st. Came under orders of the 2/1st London Mounted Brigade.
- March 1915 : moved with the brigade to Norfolk and placed under orders of 2/2nd Mounted Division.
- 20 March 1916: division renamed 3rd Mounted Division.
- April 1916 : brigade renamed 12th Mounted Brigade.
- July 1916: converted into a cyclist unit, under orders of 4th Cyclist Brigade in 1st Cyclist Division at North Walsham.
- November 1916: division broken up; merged with 2/3rd County of London Yeomanry to form 6th (1st and 3rd County of London) Yeomanry Cyclist Regiment. Moved to Reepham and came under orders of 2nd Cyclist Brigade in new 1st Mounted Division.
- March 1917: resumed identity and moved to Worstead.
- Moved by July to Overstrand.
- 4 September 1917: division renamed The Cyclist Division
- At some point, moved to Coltishall.
- May 1918: moved with brigade to Ireland and was stationed first at The Curragh then Athlone.
3/3rd County of London Yeomanry
- Formed in April 1915 as a “third line” (training, draft-supplying reserve for the 1/3rd and 2/3rd) and affiliated to 9th Reserve Cavalry Regiment at Dublin.
- Early 1917: absorbed into 2nd Reserve Cavalry Regiment at the Curragh.
In the 1917 renumbering of the Territorials, the County of London Yeomanry issued numbers from the block 265001-270000. Corps of Hussars.