Tomás Óg Mág Samhradháin (anglicised Thomas McGovern Junior) was chief of the McGovern Clan and Baron or Lord of Tullyhaw barony, County Cavan from 1584 until his death at the end of the 16th century.
His ancestry was Tomás Óg son of Brian son of Tomás (d. 1532) son of Maghnus (d. 1497) son of Tomás Óg (d. 1494) son of Tomás na Feasoige (d. 1458) son of Fearghal (d. 1393) son of Tomás (d. 1343) son of Brian ‘Breaghach’ Mág Samhradháin (d. 1298). He was the second eldest son and had two brothers who both were chiefs of the clan, Brian Óg Mág Samhradháin and Feidhlimidh Mág Samhradháin, together with a third brother Emonn of Lissanover.
On the death of the McGovern chief, Brian Óg Mág Samhradháin in 1584, Tomás took the chieftaincy and moved to the chief’s residence in Ballymagauran.
A sub-sept of the McGoverns known as the Coffey Magaurans, centered on the northern part of Tullyhaw called Largay (now the town of Blacklion) seemed to be exercising a degree of independence from the main chieftaincy at Ballymagauran as, in an Indenture dated 1585 between the Lord Deputy of Ireland John Perrot and, inter alia, Turlough McGovern of Largay, the said Turlough claimed to be chief of the McGoverns. The indenture reads-
This Indenture betwixte Perrotte, Lord Deputy Generall of Ireland, for and on the behaulfe of the Queene's most excellent Majesty of the one partye, and John Garvey, bishop of Kilmore; Lysaghe O'Ferrall, bishop of Ardaghe; Sir Briane O'Royrke of Dromahire,knt.; Cahall MConnor Carragh Magrannyll of Inishmurryne, otherwise called Magrannell of Moynishe, chiefe of his name; Tirlaghe M'Molaghline oge Magrannyll of Dromarde, otherwise called Magrannyle of Clonmologhlyne, chief of his name; Tyrelaghe Magawryne of the Largine, chief of his name; Teige oge Maglanchie of Rossclogher, chief of his name; Owyne MThelline O'Royrke of the Carre; Rory McEnawe of Inyshimylerye, chiefe of his name; Melaghlyne McOwyne McMurrye of Loghmoyltagher; Farrell MTernan of Cloyloghe; Bryan McLoghlyne of the Fayhee; Phelyne Glasse of Cloncorycke; Wonye MacSheane O'Royrke of Lloghnecouhye and Tyernane O'Royrke of Dromahyre of the other parte.