Enniscrone Castle is located to the eastern end of a small ridge overlooking the Castle Field and the town of Enniscrone: the megalithic tombs are close-by to the western end.
The history of Enniscrone Castle, also known as O'Dowd's Castle, is a long one and its location marks a strategic coastal route through Connaught into west Ulster. During the 12th century the O'Dowda ruled the kingdom of North Connacht having removed the O'Caomhain from the Enniscrone area. A number of fortifications probably existed before the first castle was built in the late 14th century. In 1512 during conflict between the Burkes of Mayo and the O'Donnells of Donegal, the Burkes captured Enniscrone Castle which was then besieged and demolished by the O'Donnells. It was rebuilt by the O'Dowda's but their power as Irish Chieftan's was waning, and with the Flight of the Earls in 1607 came the end of Gaelic Irish society.
The Mac Donnells, who were gallowglasses in the service of the O'Dowd's, sold the castle in 1597 to John Crofton. Crofton may have rebuilt the castle in a more English/plantation style, at a time when the purely defensive nature of castles was being made obsolete by the advances in artillery. The function of the house was to provide a comfortable residence that could be defended against a small-scale attack. He then sold it on to Thomas Nolan of Ballinrobe. Nolan's son John was living there in the 1635. During the rebellion of 1641 the confederates, under David O'Dowd, commandeered the castle and placed a garrison there. It was recaptured by parliamentarian troops led by Sir Charles Coote in 1645. Through the Cromwellian Settlement the castle and 65,000 acres of land were granted to Sir Frances Gore. The Gore family was succeeded by the Orme family but the castle became dilapidated and fell into ruin.
Built on a raised level platform, the castle was a rectangular gabled house with three-quarter round towers at it corners, but only the two western towers survive. The house was two storey with attics. On the ground floor there was a centrally placed doorway in the south wall that has evidence of drawbar sockets. Also on the ground floor on the west wall is a large fireplace with a small oven built onto its south side. There is a smaller fireplace on the upper storey and the chimneys are still intact. The floor levels of the towers correspond to those of the main building. A number of gun loops and small windows occur throughout the building. Stone from the castle was used in the construction of the pier.
The castle overlooks the ruins of a small rectangular church called Valentine's church. It is possibly on the site of Cill Insi, an older ecclesiastical site which was still standing in 1666. The church was rebuilt sometime around 1679. In 1712 Thomas Valentine from Lancashire was appointed to this area as Protestant vicar. He died in 1765. The church was damaged during the 1798 rebellion and was not used again.