The castle came into the possession of Michael Cusack of Portraine, County Dublin, through his marriage to Margaret Dexter sometime before his death in 1589. Their union is commemorated on a stone cross that once stood along the old road to Rathaldron, about 700 metres southeast of the castle itself.

By 1640, the property had passed to Patrick Cusack, who controlled 260 acres in Donaghmore parish that included not just the castle but also a mill and a weir, making it a significant economic hub along the river. The Civil Survey of 1654–6 documented these holdings, providing a snapshot of the estate during a turbulent period in Irish history when such surveys were conducted to assess lands following the Cromwellian conquest.

The castle underwent significant transformation in the early 19th century when Gothic Revival architecture was all the rage amongst Ireland's landed gentry. Castellated wings were added to the southeast and southwest, turning the medieval tower into a more comfortable dwelling whilst maintaining its romantic character. The original four-storey tower still forms the heart of the building, complete with its vaulted ground floor ceiling; a defensive feature common in Irish tower houses. Though many windows were remodelled into fashionable pointed Gothic arches during the renovation, some original window openings survive in the south and west walls, offering glimpses of the castle's medieval past. Remarkably, Rathaldron remains an occupied residence today, a living link to centuries of Meath's history.