Their seat was the castle of Harrenhal, which was granted to their founder, the Targaryen general Quenton Qoherys, by Aegon the Conqueror as a reward for his service in the War of Conquest. However, the Qoherys' eventually became extinct, and the castle was passed on to House Harroway.
In the books
Quenton Qoherys had previously served as the Master-at-Arms at Dragonstone. His line did not last long, however. He was succeeded by his grandson Gargon, known as Gargon the Guest due to his habit of visiting every wedding in his domain and claiming the lord's right of first night that allowed him to bed the bride. During a rebellion by Harren the Red, self-proclaimed grandson of Harren the Black, the father of a maid whose virginity had been taken by Gargon allowed Harren to enter Harrenhal. Harren then gelded and murdered Gargon, and all of the castle's inhabitants were put to the sword, rendering House Qoherys extinct. They were replaced as the rulers of Harrenhal by House Harroway.
Houses from the Riverlands