The State Apartments dominate the Southern Range of the Upper Castle Yard or Great Courtyard. They were formerly the private and public rooms of the Viceroys and the Viceregal Court, the seat of the executive and the focus of fashionable social life.

The State Apartments can be made available for a very limited number of appropriate private functions of up to 202 guests for dining or up to 400 for receptions. Access is by means of the doric colonnade and the imperial staircase. St. Patrick's Hall is one of the most significant and prestigious public rooms in Ireland. Here the inaugurations of the Presidents of Ireland take place, as do other important State functions including State Banquets for visiting Heads of State