Rathdown (Irish: Ráth an Dúin) is a barony in County Wicklow, Ireland.

Rathdown barony derives its name from Rathdown Castle, located near Greystones (Irish: Ráth an Dúin, "rath of the dún"; anciently Ráth Oinn).

[1] Rathdown barony is located in northeastern County Wicklow, east of Kippure, north of the Glen of the Downs, south of the County Dublin border and opening onto the Irish Sea around Bray Head.

The Uí Briuin Cualann are noted very early here, with their territory extending into southern County Dublin.

This article related to the geography of County Wicklow, Ireland is a stub.