The first houses in Mullinahone grew up around the Norman castle, Killaghy Castle, whose history can be traced back to around the year 1206. What we see of it today is in two parts, the old castle, four storeys high, built in the 15th or the 16th Century and called a tower-house. During Tudor times a long house was added and in the 18th Century there was two more buildings including a Manor House attached to the old castle. Today it is in use as a Guest House.