The castle is rectangular in shape with massive square towers at each corner. The main block has four storeys, the towers have five. There is a fine Renaissance door in the first floor on the north side and a more traditional pointed door on the ground floor on the south side. The flat ‘Burgundian’ arch is a feature of the ground-floor windows, while those on the upper storey and Tudor with two or three mullion. The castle has a remarkable number of well-preserved fireplaces. This building is an interesting combination of the traditional Irish tower-house architecture with pointed arches and the new Tudor architecture with Renaissance doorways and mullioned windows.
Kanturk town is the capital of the ancient Barony of Duhallow. The Castle was built for MacDonogh MacCarthy, Lord of Duhallow around 1601 as a defence against the English. But news of its building reached England where the Privy Council, being uneasy about its purpose, ordered that building work should stop, possibly as a result of the disastrous Battle of Kinsale or possibly because MacDonagh could not borrow any more money from English moneylenders. So the castle was probably never completed. Dermot MacCarthy, into whose hands it later came, mortgaged it in 1641 to Sir Philip Perceval who after taking possession took out many of the fixtures and fireplaces to be placed in another of his properties.
The castle was donated to the National Trust Committee for Ireland by Lucy, Countess of Egmont on May 8th, 1900 under the condition that it be kept in the same condition as it was when handed over, i.e. a ruin. Kanturk Castle holds an interesting position within the National Trust movement. It was only the 9th property acquired by the National Trust and was declared inalienable under the 1907 Act. On 14th July 2000 the property was handed over to President McAleese on behalf of An Taisce, for the Irish people, at a well publicised event on the grounds of the castle following amended legislation in Westminister.