One scholar gives 1765, another 1756, and the discrepancy has never been fully resolved. That small uncertainty is fitting for a building that rewards close attention: the two main facades are constructed from entirely different materials, the southern entrance front faced in brick with stone detailing, the northern view front in ashlar limestone with sandstone trim, so that the house presents a different character depending on which direction you approach it.

The house was designed by Davis Duckart for Abraham Devonsher. Duckart, a Sardinian-born architect who worked extensively in Ireland during the eighteenth century, was responsible for several significant buildings in Limerick and elsewhere, and Kilshannig is considered among his finest domestic commissions. The northern front, which looks out towards Rathcormack, is arranged over a basement with semicircular windows glazed as fanlights, a central breakfront of three bays, and shouldered architraves framing the first-floor windows. L-shaped wings, connected to the main house by a corridor with blind pilastered arcades, extend along the northern elevation. Inside, the plasterwork is the great prize: the Francini brothers, Swiss-Italian stuccadores who worked across Ireland and England during the mid-eighteenth century, contributed rococo plasterwork of considerable quality, the kind of extravagant, fluid ceiling decoration in which figures, foliage, and ornamental framing blur into one another. The western wing is now derelict. Elsewhere on the estate, a cluster of ancillary structures survives: an ice house, a coaching house, renovated farm buildings, two walled gardens to the east, and, to the south, a dog kennel complex with a feeding tower and archway, a reminder of the organised, hierarchical world the house was once built to command.