Arthur James Plunkett, 9th Earl of Fingall KP PC (I) (29 March 1791 – 21 April 1869) was an Irish peer, styled Lord Killeen from 1797 to 1836. He became Earl of Fingall in 1836 on the death of his father the 8th Earl and was appointed a Knight of the Order of St Patrick on 9 October 1846. His mother was Frances Donelan, daughter of John Donelan of Ballydonnellan, County Galway and his wife Mabel Hore. Like his father he was a convinced supporter of the cause of Catholic Emancipation. Both father and son worked for years with Daniel O'Connell to achieve it.