| 16161 | Birr Castle Archives | A-W | 1804 | C/10: Letter to Sir William Parsons from Edmund Malo... | The Rosse Papers |
| 16162 | Birr Castle Archives | A-W | 1804 | D/2/1-18: Letters to Sir William Parsons from Peter ... | The Rosse Papers |
| 16197 | Birr Castle Archives | A-W | 1802-1804 | H/92: Letters and papers of Lord Hawke regarding the... | The Rosse Papers |
| 14586 | Cashel and Emly Diocesan Archives (RC) | | 1804 | 1804: 4 - Dr Power to Bray. Bray has been appointed ... | Papers of Dr T. Bray, Archbishop of Cashel and Emly, 1792-1820 |
| 16740 | Cashel, Ferns and Ossory Diocesan Archive (CoI) | | 1804-1877 | Doon Church Parochial Records (Transcript of baptism... | Bolton Library Archive |
| 16832 | Cashel, Ferns and Ossory Diocesan Archive (CoI) | | 1804-1816 | 1 envelope, 9 sheets containing information on: Mago... | Bolton Library Archive |
| 12516 | Limerick Museum | AQNO (0000.2056) | 1804 | Book. Limerick printed by John and Thomas McAuliff. ... | |
| 14112 | Louth County Archives | | 1804-1829 | John Henry, Letterbook, possibly rent collector or a... | |
| 20208 | Meath Local Studies and Family History Department | Box I/ | 1804 | 19 Map of Butlerstown Estate of Thomas Bligh by Hugh... | Mountainstown Documents |
| 22896 | Methodist Historical Society of Ireland | | 1784
1804
1823 | Archival box 9, contains sermons and obituaries. For... | |
| 3953 | National Archives of Ireland | Soc1026/29 | 1804 | Series 1: Ball, Charles, Dublin, enclosing Honora Bo... | State of the Country Papers |
| 4008 | National Archives of Ireland | 1/145 | 1804 | Villiers, Lady Sarah Sophia, to Lord Westmoreland. H... | Westmoreland Correspondence |
| 4967 | National Archives of Ireland | | 1798
1804 | 1798 Rebellion Papers in the Quit Rent Office Collec... | Quit Rent Office |
| 1482 | National Library of Ireland | Ms1554 | 1791-1804 | Alphabetical list of donators and subscribers to Ple... | |
| 1497 | National Library of Ireland | Ms2069 | 1804-1806 | Includes two letters from Mary Ann Bulkley to her br... | |
| 2016 | National Library of Ireland | Ms8123 | 1804-1827 | Miscellaneous letters includes letters of Rev. P J P... | Plunkett Papers |
| 2403 | National Library of Ireland | Mss31540 (1-2), 31,561-56 | 1789-1804 | Nine letters from Dominick Trant to his wife, Eleano... | Trant Papers |
| 2409 | National Library of Ireland | Mss9611-9414 | 1752-1804 | Dowager Lady Midleton's Account Books: 1752-1781 178... | Brodrick Papers |
| 2590 | National Library of Ireland | Ms4928 | 1804-1814 | Servants' Wages Book of the French family of Monivea... | |
| 3000 | National Library of Ireland | Mss9411-9414 | 1752-1804 | The dowager Lady Midleton's accounts in four volumes... | Brodrick Papers |
| 3038 | National Library of Ireland | Ms9878 | 1804 | Charges in scale for attendance and medicine agreed ... | F.S. Bourke Collection |
| 3459 | National Library of Ireland | Ms10371 | 1804-1826 | 19 letters to Letitia Balfour, 1825-1826 and 8 lette... | Townley Hall Papers |
| 3516 | National Library of Ireland | Mss11081-11082 | 1804-1814 | Miscellaneous letters, 1804-1814. These include lett... | Grogan Papers |
| 10760 | National Library of Ireland | Ms 19967 | 15 May 1794-1 June 1804 | Domestic and personal account book kept by Lady Eliz... | Mahon Papers |
| 10801 | National Library of Ireland | Ms20739 | 1804 | Two letters of Daniel O'Connell to his wife containi... | |
| 6367 | Public Record Office of Northern Ireland | T/1766 | 1804-1983 | T/1766/1 Genealogical notes on the Heron and Hutton ... | |
| 7134 | Public Record Office of Northern Ireland | D/2896 | 1804-1976 | The papers of the Holy Trinity Church, Lisnaskea, Co... | |
| 7308 | Public Record Office of Northern Ireland | D/3649 | 1804-1902 | 2 volumes of rentals of the estates of Mrs Ellison-M... | |
| 7911 | Public Record Office of Northern Ireland | T/1195/1 | 1804-1953 | Copy of a skeleton abstract of pedigrees relating to... | |
| 8029 | Public Record Office of Northern Ireland | T/1560/1 | c.1804 | Fragment of a draft letter written by Revd. James Fo... | |
| 8406 | Public Record Office of Northern Ireland | T/2627 | 1791-1804 | T/2627/5/U/21 Copy of a memorandum relating to req... | |
| 8612 | Public Record Office of Northern Ireland | T/521/1 | 1804-1806 | Copy of a list of passengers travelling from Ireland... | |
| 844 | Religious Society of Friends in Ireland Historical Library | QMI/H65-69 | 1804-1840 | Schools and Education: QMI/H65 Proceedings of the C... | Leinster Quarterly Meetings |
| 1274 | Religious Society of Friends in Ireland Historical Library | MMI/Z1 | 1804-1824 | Miscellaneous: Quarterly Meeting of Women Friends he... | Carlow Monthly Meeting |
| 1334 | Religious Society of Friends in Ireland Historical Library | MMVI/L1 | 1749-1804 | Wills and Inventories: Certificates of Removal, Will... | County Wexford Monthly Meetings |
| 4166 | Religious Society of Friends in Ireland Historical Library | Deed Box XII | 1803-1804 | Elizabeth Cope, wife of William Cope: Folder 9:3 Pa... | Deeds |
| 5322 | Religious Society of Friends in Ireland Historical Library | MMVI/K1 | 1804-1816 | Removals: Copies of Certificates of Removal, 1804-18... | County Wexford Monthly Meetings |
| 11097 | Religious Society of Friends in Ireland Historical Library | PM/TipI/J1 | 1804 | Clonmel Preparative Meeting, Women's Meeting Cash Bo... | |
| 22401 | Royal College of Physicians of Ireland | | 1804-1843 | Cow Pock Institution Subscription Book,, 1804-1843. | Kings and Queens College of Physicians |
| 10186 | Trinity College Dublin, Manuscripts and Archives Department | TCDMs5889 | 1804-1837 | Diary, 1804-1837, of Margaret Synge, née Wolfe, Fou... | |
| 10227 | Trinity College Dublin, Manuscripts and Archives Department | TCDMs7307/1-22 | 1804-1812 | Letters of Lady Ann Clements to Austin Cooper, 1804-... | Clements Papers |
| 18399 | University of Galway Archives | LE15 | 1804-1858 | A chronologically arranged list of five deeds relati... | Kelly and D'arcy Deeds |
| 19438 | Westmeath County Archives Department | | 1804-1816 | Common Council Book, Borough of Athlone:24 June 1804... | |