Ardagh (Irish: Ardach) is a barony in County Longford, Ireland.

Ardagh barony derives its name from the village of Ardagh, County Longford (from Árd-achadh, "high pasture").

Ardagh barony is located in eastern County Longford.

Ardagh barony was formed from the territory of Sleughtwilliam (Edgeworthstown), the territory of Clangillernan (Templemichael), and from part of the church lands in the parishes of Ardagh and Ballymacormick.

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