21st Cavalry may refer to:
Divisions 21st Cavalry Division, United States
Brigades 21st Cavalry Brigade, United States
Regiments 21st Alberta Hussars 21st Cavalry Regiment (United States) 21st Horse (Central India Horse) 21st Lancers 21st Prince Albert Victor's Own Cavalry 21st Regiment of (Light) Dragoons XXI Corps Cavalry Regiment
American Civil War units Union Army 21st New York Cavalry Regiment
Confederate Army 21st Texas Cavalry Regiment 21st Virginia Cavalry Regiment
Companies 21st (Cheshire) Company, Imperial Yeomanry
See also 21st Division (disambiguation) 21st Brigade (disambiguation) 21st (disambiguation)