Map showing approximate boundaries of Poor Law Unions & Civil Registration Districts (Superintendents Registrar’s Districts) for Dublin city and County overlaid on 1902 map from Thom’s directory, details derived from townland index data.

Dublin City and County Poor Law Unions & Civil Registration Districts (Click to view or download a large version)
Note : several of these districts extend into adjacent counties – Rathdown into North County Wicklow, Naas into County Kildare, Dunshaughlin into County Meath, and Celbridge into County Kildare plus a small of part County Meath.
Original map shows Baronies and is available at this link.