Clonmacnowen (; also Clonmacnoon) is a historical barony in eastern County Galway, Ireland.
Baronies were mainly cadastral rather than administrative units. They acquired modest local taxation and spending functions in the 19th century before being superseded by the Local Government (Ireland) Act 1898.
The name derived from Irish , "clan of the son's of Eoghan," referring to a son of Domnall Mór Ua Cellaigh, a king of UàMaine who died in 1221.
The O'Muldoons (àMaoldúin) of Aughrim were ancient rulers of the area as chiefs of Eoghanacht Ani (Eóganachta of Aidhne).
By 1585 Seán na Maighe àCellaigh was the owner of the area.
Clonmacnowen barony was created before 1672. It appears in the Down Survey (1665âÂÂ66) as Clanemtoneen.
Clonmacnowen is in the east of the county, where the River Suck forms the border with County Roscommon.
Settlements within the historical barony of Clonmacnowen include: