Clonalis House:

Clonalis House, just west of the town, is the ancestral home of the Clan O'Conor, the last High Kings of Ireland. The dynasty gave eleven high kings to Ireland and twenty four kings to Connacht. The family traces back to Feredach the Just in 75 A.D. and is Europe's oldest recorded family. The 45 room mansion was built in 1878 and contains a priceless collection of archival material, illustrating a tradition going back 60 generations.

The town also has "Hell's Kitchen" the only pub in Ireland with a train inside. Hell's Kitchen also contains a Railway Museum, probably the most unusual museum building in Ireland. Sean Browne’s railway museum includes a 1955 A55 diesel locomotive. It is open 7 days a week and is a treasure trove for railway enthusiasts. On display are bells, lamps, shunting poles, signal equipment etc. The museum has no official links with Castlerea railway station.

Castlerea has a rich history producing the last High King of Connaught as well as the first President of Ireland. The present town of Castlerea was built in the 14th century.  Previous to this the town was situated in Ballinapark in Arm townland on the Galway road less than a mile from the present town.  Some of the ruins of houses from the 'oldtown' as well as the church can still be seen.  One of the earliest records of a settlement is when a monastery was formed at Kilkeevan by Saint Patrick in 433-434.  This monastery was entrusted to St. Kevin thus the name Kilkeevan.  It continued to be a place of worship until the year 1537 and is still used as a burial ground to this day.

Castlerea is the home the O' Connors the last high kings of Connaught.  Clonalis house which is situated on the outskirts of the north west of the town is the ancestral home of this great Irish family.  However the 'new' house at Clonalis was only the most recent manifestation of the built heritage of the O'Connor's over the past 1500 years.  In the library at Clonalis can be seen the pedigree completed by Sir William Betham, the Ulster King at Arms, in 1823 . This pedigree of the O'Connor's lists 11 High Kings of Ireland and 26 Kings of Connaught since the time of Christ. The Coronation Stone or Inauguration Stone of the O'Connor's can still be seen at Clonalis to this day.

The 'New' Clonalis House now serves the dual purpose of being a family home and a major repository of heritage and history, containing correspondence, heirlooms, objet d'art and portraits of the O'Connor's over the past 600 years. The Clonalis Library, containing some 7000 volumes, is widely considered to be one of the best collections in private ownership in Ireland