Thomas Blennerhasset was granted an estate in about 1615 and established a castle at Crevenish which is about 2km to the south west of Kesh. The castle described as 'as a bawn of lime and stone 23m long and 14m broad, and about two and a half storeys high'. A salient angle tower in the NW corner is now four storeys high, with gun loops on each face. The remains suggest that it may have been enlarged at a later date. Part of the flanker balancing on the NW tower is built into a farm shed.
Thomas Blennerhasset's son died in 1629 and his widow married Rory Maguire. Before 1641, Rory Maguire was well thought about, even by the planters, and after his marriage Crevenish Castle was a rendezvous for both Irish and English

Events overtook the status quo at Crevenish Castle. In 1641 the October campaign began to recover land and property. Rory Maguire planned to capture the planter gentry and for this purpose invited them to dinner at the castle. By then he had become well respected and the invitations were accepted. Treachery intervened to assist the guests and an informed Cole, Governor of Enniskillen, came to the castle with considerable apprehension. When advised that ' his horse would be ready in 10 minutes', he and the other guests made good their escape.
In the late 17th century parts of the castle were used as a church and the bawn as a graveyard. Lady Deborah Blennerhasset Maguire is reputed to be buried within the bawn.
The castle ruins are in private care.