Castle Leoch is the fictional seat of Clan MacKenzie, located in the northern Scottish Highlands.
Jacob MacKenzie seized the castle in 1690 from Donald MacKenzie, who was absent from the castle at the time and subsequently died under mysterious circumstances. Jacob married Donald's widow, who bore him six children.
Upon Jacob's death, his eldest son Colum MacKenzie took leadership of the clan. His suitability came into question, however, when as a young man Colum suffered several injuries to his legs that healed badly, and left him permanently disfigured. His younger brother, Dougal, was a likely contender, but the brothers stuck by each other, and Colum retained control as laird while Dougal took on the duties of war chief.
Colum's son, Hamish, would have become chief of the clan upon Colum's death, were it not for the Jacobite Rising of 1745. Although Colum had petitioned for a matriculation of arms, his claims were disputed by heirs of Donald MacKenzie of Leoch, and the matter of the title was never resolved. In any case, the crown seized the MacKenzie lands after the Rising, and Hamish emigrated to Nova Scotia shortly thereafter. Eventually the lands reverted to a distant heir of Donald MacKenzie: Jeremiah MacKenzie. By the 20th century, the castle itself lay in ruin.
After Jacob MacKenzie took control of the castle, he lived there with his wife, Anne, and their children: Ellen, Colum, Dougal, Janet, Flora, and Jocasta. Colum continued to reside there for the rest of his life with his wife, Letitia, and son Hamish. Dougal lived there intermittently, having another residence called Beannachd where his wife and family lived.
Three of Jacob's daughters survived to adulthood, and each left the castle upon their respective marriages. Ellen's son, Jamie, lived at the castle for a time when he was sixteen, as was the custom of the time. Some years later, Jamie returned to the castle, this time seeking refuge from the crown, who had placed a price of ten pound sterling on his head for the murder of an English prison guard.
- Cobhar - the horse that Jamie lets Hamish ride after stopping him from trying to ride Donas. Cobhar is a bay.
- Donas - described as a "huge, evil-tempered sorrel stallion". Jamie and Auld Alec are breaking in Donas at Castle Leoch. Jamie rides Donas to rescue Claire from the witch trial and Donas's speed allows him to get there on time. Young Fergus is sent on Donas to deliver the Deed of Sasine safely to Jenny and Ian. The name Donas is given to all the sorrel colts descended from the original Donas. When Claire returns through the stones there is another horse called Donas at Lallybroch who is Donas's grandson.
- Losgann - the mare that had trouble foaling at Castle Leoch.
- Mahomet - a stallion that Auld Alec wants Jamie to help him geld.
- It was only after she had created Castle Leoch for the series that Diana Gabaldon learned of the real life seat of Clan MacKenzie – Castle Leod.
- In the television adaptation, Doune Castle was used as the exterior of the fictional Castle Leoch. Production designers used molds of the architecture at Doune Castle to build sets at the studio, where the interior castle shots were filmed.
- Doune Castle may look familiar to fans of Monty Python and the Holy Grail. The castle was used extensively during the filming of the 1974 movie.