The State Apartments in Dublin Castle were originally constructed as living accommodation for the Lord Lieutenant. The Lord Lieutenants preferred the comforts of the Phoenix Park residence however and tended to live there except for Castle Season when a series of Balls and events was held for fashionable society at the castle. The Apartments are now only used for State occasions notably the Inauguration of a new President and during the Irish Presidency of the European Union. The series of ornate highly decorated rooms stretch along the first floor of the southern range of the upper yard.

There are many other important rooms, notably the Wedgwood Room, an oval room decorated in Wedgwood Blue with details picked out in white. It was used as a Billiards Room in the 19th century.