 The Fír Lemna (also known as Uí Tuathail and Síl Tuathail) are cited as being one of the "Trí Tuatha of Oirghialla" alongside the Uí Chremthainn and Síl Dubthir.Its territory is thought to have been near Clogher, Co. Tyrone.The region of Magh Lemna is given as being in the parishes of Clogher and Errigal Keerogue in southern Co. Tyrone bordering Co. Monaghan.