During the first half of the nineteenth century, Yeomanry Regiments were used extensively in support of the civil authority to quell riots and civil disturbances (including the Peterloo Massacre), but as police forces took over this role, the Yeomanry concentrated on local defence.
During the Second Boer War, companies of Imperial Yeomanry were formed to serve overseas from volunteers from the Yeomanry. In 1901 all yeomanry regiments were redesignated as "Imperial Yeomanry", and reorganised.
Following the First World War the Territorial Force was redesignated as the Territorial Army. Following the experience of the war, only the fourteen senior yeomanry regiments retained their horses, with the rest being reroled as armoured car companies, artillery, engineers or signals. Two regiments were disbanded. The converted units retained their yeomanry traditions, with some artillery regiments having individual batteries representing different yeomanry units.
On the eve of the Second World War the Territorial Army was doubled in size, with duplicate units formed, this led to some regiments being de-amalgamated. The last mounted regiment of yeomanry was the Queen's Own Yorkshire Dragoons, who were converted to an armoured role in March 1942. Volunteers from the Yeomanry served in the Long Range Desert Group from 1940 through to 1943, incorporated into "Y Patrol".
There were reductions in the size of the TA in 1957 and 1961 and this led to amalgamation of some pairs of yeomanry regiments. There was a major reduction in reserve forces in 1967 with the formation of the Territorial and Army Volunteer Reserve, and all existing yeomanry regiments were reduced to squadron, company or battery sub-units. A number of further reorganisations have taken place in the intervening years.