King John's Castle

King John's Castle may refer to:
 * King John's Castle (Limerick), Limerick City, Ireland
 * King John's Castle (Carlingford), County Louth, Ireland
 * King John's Castle (Kilmallock), County Limerick, Ireland
 * King John's Castle in Kineton, Warwickshire, United Kingdom
 * King John's Castle, a horse that finished second in the 2008 Grand National