Conolly's Folly, Stone obelisk monument in Maynooth, Ireland

Conolly's Folly is a 42-metre obelisk of grey, rough-textured stone, designed by Richard Castle, standing between Celbridge, Leixlip and Maynooth in County Kildare. A tapering obelisk pillar rises from a gabled central block with a round-arched niche, set over a wide base pierced by a large central arch and two smaller flanking arches. Stone pineapples and eagles adorn the structure, and four urns stand on short pillars at the corners of the base.

Katherine Conolly, widow of Speaker William Conolly, commissioned the folly in 1740, after a severe winter, to give work to the poor of Celbridge during the famine of 1740–41; it cost £400. Richard Castle designed it, and it stood on land belonging to Carton, home of the FitzGerald family, Dukes of Leinster, not on the Conolly estate. The Irish Georgian Society restored it between 1962 and 1965, its first major project.

The name Conolly is spelled with one n, as used by William Conolly and his descendants, from the Irish Uí Conghaile. The folly appears on the emblem of the Irish Georgian Society, which restored it between 1962 and 1965, and Mariga Guinness, the society's co-founder, is buried on the site. An Irish 10-pence stamp issued on 6 December 1978 carried an image of the folly.

The Office of Public Works has fenced the structure, so visitors cannot walk up to the arches or climb the internal stair to the viewing level. It stands on 5 acres of woodland between Celbridge, Leixlip and Maynooth, reached by minor roads; the obelisk is best seen from a distance, framed by the trees.

The obelisk stands on land that belonged to Carton, home of the FitzGerald family, Dukes of Leinster, not on the Conolly estate itself. A staircase inside climbs to a viewing level. On 6 December 1978 Ireland issued a 10-pence stamp showing the folly.