The 1st Mounted Division was a Yeomanry Division of the British Army active during World War I. It was formed in August 1914 for the home defence of the United Kingdom from four existing mounted brigades of the Territorial Force, each of three regiments of Yeomanry. The divisional order of battle changed often, as the 1st Line brigades left for service overseas and were replaced by 2nd Line formations. It was converted to the 1st Cyclist Division in July 1916, and was broken up in November 1916 without being involved in active service. It remained in East Anglia throughout its existence.