The Three Tuathas () was a name of a kingdom consisting of three kingdoms in County Roscommon, Ireland lying between Elphin and the River Shannon. It extended from Jamestown on the River Shannon to the north portion of Lough Ree. It was divided into three kingdoms known as Cenél Dobtha between Slieve Bawn and the River Shannon; Corca Achlann to the west and Tir Briuin na Sinna to the north. The O'Monaghan's and O'Boyle's were rulers of the Three Tuathas in the 13th century.