Situated in the beautiful Blackwater Valley and commanding a superb position overlooking the river Blackwater this is one of the most delightful parts of Ireland. King John who later handed it over to the church originally built Lismore Castle. It remained a Bishop's Palace until 1589 when it was acquired by Sir Walter Raleigh and then sold on to Richard Boyle, first Earl of Cork, in 1602.

This well-known castle was renovated and extended several times throughout the centuries, is now the property and temporary residence of the Duke of Devonshire’s. It derives its name from the 'Ráth' now known as the 'Round Hill', but in former times as 'An Líos Mór' and as some scholars would assert in pre-Christian times as 'Dún Scéinne'. It was built or rather rebuilt by King John (The Earl of Morton) in 1185 as prior to this, it was probably originally built by the orders of Henry 2nd, who visited Líos Mór in 1171. Milo De Cogan and Robert Fit Stephen were sent by him to choose a site for a stronghold as protection against the 'mere Irish'. In 1181 Culann O' Cuileáin and Ó Faolaín, Prince of Na Déise, attacked and destroyed the castle and killed about 60 of its garrison.

The entrance to the castle is by the 'Riding Gate' so called from its having formerly been guarded by two mounted sentries, the niches for the horses still being shown. The castle has a number of towers. King John's Tower is situated to the right of the entrance and the Carlisle Tower on the left and is about 245' in height. Stone for the parts of it and for other parts of the castle, we were told, were at Chatsworth, England, and were brought over in specially chartered vessels.

There is also Sir Walter Raleigh's Tower. This tower was probably part of the ecclesiastic building. The castle was for a long time the residence of the Bishop's of Lismore. Miler Macgrath, Archbishop of Cashel rented it to Sir Walter Raleigh in 1589 for the sum of £13-6-8 per annum. It passed later to Sir Richard Boyle, 1st Earl of Cork and it is here that the philosopher Robert Boyle was born in 1686. There is also the Flag Tower, which flanks the northeast angle. The drawing room contains a large bay window over hanging the river, known as 'King James' Window. While dining in the castle on 1689 he approached this window but started back when he saw the depth below.

Lismore Castle had to withstand several sieges in its long and chequered history. It was attacked and besieged three times during the civil wars of 1641-1649.

When the 4th Earl of Cork died, without male heirs in 1753 the ownership passed to his eldest daughter Lady Charlotte who had married the 4th Duke of Devonshire in 1748. It thus passed to the Devonshire family who still own it.

During the renovation in 1814 the valuable manuscript now known as the 'Book of Lismore' but really the 'Book of Mac Cartach Riabhach' and the 'Lismore Crozier' were found in an excellent state of preservation. They are now in the National Museum in Dublin.

The castle gardens are set on 7 acres of land within the castle's 17th century outer defensive walls. The gardens have many magnolias, camellias and rhododendrons and are open to the public from mid-April to early October between 1.45pm and 4.45 pm. The gardens are believed to be the oldest in Ireland retaining much of their original Jacobean form.