The ‘Philadelphia Papers’ are six volumes of Irish State Papers from the 1600s, containing letters from the king to his deputy in Ireland about the Plantation of Ulster, when settlers (planters) from Scotland and England took over land confiscated from Irish owners accused of treason.
In the 1700s a historian took these volumes from Dublin Castle to write a history of the plantation, but he never gave them back.
Later they found their way across the Atlantic to the Library Company of Philadelphia. In 1867 a scholar recognised them as the missing Irish records and arranged for their return. Five volumes were sent to the new Public Record Office in Dublin—only to be destroyed in 1922.
Fortunately, in 1867 when the five volumes arrived from America they were copied out in full. These copies were preserved by the Public Record Office, London, now The National Archives UK. The title page inside the first volume tells the whole story of how they were ‘restored to the British Nation’. A sixth original volume never left Philadelphia and so was not destroyed in 1922. To mark the centenary of 1922, all six volumes — the surviving original in Philadelphia and the five duplicates preserved in London — have been digitised and can at last be reunited on screen.