The Folly was built within the Castleton Estate (containing Castleton House, which contains two follies, both commissioned by Katherine Conolly, the philanthropic widow of Speaker William Conolly, to provide employment for hundreds of the poor of Celbridge when the famine of 1740 - 41was at its worst. The Obelisk was built in 1740 after a particularly severe winter.
As a folly, it could be seen from the back of Castletown some 4 kilometres (2.5 miles) away and it is built exactly perpendicular to the house. It was intended to mark the rear entrance gateway to Castletown house in conjunction with an avenue leading to the house.
The folly was built on land that was near to, but not on, the Conolly estate. It therefore belonged to neighbouring Carton, the home of the FitzGerald family, Dukes of Leinster.
Designed by Richard Castle, it is 42 metres (140 feet) high and is composed of several arches, adorned by stone pineapples and eagles, topped by a massive obelisk pillar. It was restored in 1965 by the Irish Georgian Society.
According to the Irish Georgian Society, the Folly was acquired in 1960 (then in a ruinous state) thanks to the generosity of Rose Saul Zalles. Its restoration was the Society's first major project.