Rathdown, County Dublin

Rathdown (Irish: Ráth an Dúin) is the south-easternmost barony in County Dublin, Ireland. It gives its name to the administrative county of Dún Laoghaire–Rathdown. Before County Wicklow was shired in 1606, Rathdown extended further south: it was named after a medieval settlement which grew up around Rathdown Castle, at a site subsequently deserted and now in County Wicklow in the townlands of Rathdown North and South, north of Greystones. The Wicklow barony of Rathdown corresponds to the portion transferred to the new county; although both divisions were originally classed as "half baronies", in the nineteenth century the distinction between a barony and a half barony was obsolete.

After the Irish Poor Law Act of 1838, the poor law union of Rathdown covered a similar area to the Dublin and Wicklow baronies combined; after the Local Government (Ireland) Act 1898, the Dublin portion of the poor law union comprised the rural district of Rathdown No. 1 and the urban districts of Blackrock, Dalkey, Killiney & Ballybrack, and Kingstown (later renamed Dún Laoghaire). The barony of Rathdown also included part of the poor law union of Dublin South, comprising after 1898 parts of the rural district of Dublin South and the urban district of Rathmines & Rathgar.

Between 1836 and 1842, the boundaries of the County Dublin baronies were regularised, by which detached portions of baronies were transferred to the surrounding barony. Civil parishes wholly or partly within the barony are:Booterstown, Dalkey (transferred from Uppercross in 1842), Donnybrook, Kilgobbin, Kill, Killiney, Kilmacud, Kiltiernan, Monkstown, Oldconnaught, Rathfarnham (mostly transferred from Newcastle in 1842), Rathmichael (two townlands transferred from Newcastle in 1842), Stillorgan, Taney, , Whitechurch.

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