The 21st Light Dragoons was a cavalry regiment of the British Army. It was raised on 5 April 1760, as the 21st Light Dragoons (Royal Forresters) by John, Marquis of Granby, and Lord Robert Sutton. It was also sometimes known as the Royal Windsor Forresters. This first regiment was however disbanded on 3 March 1763.
It was raised again in 1779 by Major-General Douglas and disbanded in 1783. Another regiment was raised in 1794 when it was also known as the Yorkshire Light Dragoons and disbanded again after the Napoleonic Wars in 1819.
In India another 21st regiment was raised in 1862, by renaming the 3rd Bengal European Cavalry, which eventually became the 21st Lancers, but they have no affiliation to the 21st Light Dragoons.