Clarmallagh (Irish: Clár Maí Locha) is a barony in County Laois (formerly called Queen's County or County Leix), Ireland.

Clarmallagh means "Flat land of Maigh Locha [lake plain]", referring to Grantstown Lake.

Clarmallagh is located in south County Laois, to the south of the River Gully, and to the north of the County Kilkenny border. It contains the lower part of the Erkina River where it drains into the River Nore.

Clarmallagh barony was anciently the northernmost part of the Kingdom of Osraige (Ossory).

In the early 12th century, Finn Ua Caellaide ruled Magh Locha (Clarmallagh) separately from the rest of Ossory.

It was ruled by the Ó Faoláin (Phelan).

It is referred to in the topographical poem Tuilleadh feasa ar Éirinn óigh (Giolla na Naomh Ó hUidhrín, d. 1420):

I Muiġ Laċa na learg te
Ó Faoláin, fearḋa an fíne
Mór an dúthaiġ as díol dáiḃ
Do lín futha Ó Faoláin