The castle was built in 1622 by Sir William Parsons. The original name give to the area was Bellamount ("beautiful mount") in reference to the pre-existing mound (Bronze Age grave). In the early 18th century Ballymount Great was home to Mr John Butler, son of Sir Toby Butler, Solicitor General for Ireland to King James II. It is John Butler who is reputed to have built the folly (sham ruin) for his daughter’s wedding day. It was never a fully built structure but as the name implies a fake ruin. Beranger drew it[where?]in 1767.
At the end of the 18th century the lands of Garranstown and Kingswood merged under the ownership of the Cullen family. The house retained the name Whitehall given to it by Mr Theo White. In William Duncan’s maps of the County of Dublin, the area is shown bearing both names, a practice that is still carried on with maps to this day. In 1865 Andrew Cullen Tynan, father of the poet and writer Katharine Tynan, inherited the farm from an uncle.