It was opened to the public in 1967 after the Forest Service of the Department of Agriculture purchased the land from the Annesley family.

Work to restore and conserve a number of areas, including the greenhouses and the Moorish Tower, was carried out between 2012 and 2014.

[7][8] It stands close to the entrance of the arboretum overlooking Castlewellan Lake and was built on the site of an old church.

The castle was built by The 4th Earl Annesley, who commissioned the Scottish architect William Burn to design it.

His son, Francis, 6th Earl Annesley, inherited in 1908 but was killed in the First World War in 1914, after which the earldom passed to his cousin Walter and the Castlewellan Estate to his sister, Lady Mabel.

It was first started in 1740 and contains trees from Asia, Australasia, and North and South America, including Japanese Maple and Giant sequoia planted in the 1850s.

They were from a group of seed collected in California by renowned plant collector William Lobb and grown in a nursery from 1853.