Thomas mac Edmond Albanach de Búrca, 2nd Mac William Íochtar (Lower Mac William or Mac William Bourke) (died 1402) was an Irish chieftain and noble who was lord of Lower (North) Connacht, Ireland.

A son of Sir Edmond Albanach de Burgh, 1st Mac William Íochtar (d.1375) and Sadhbh Ní Mháille (daughter of Diarmuid mac Owen Ó Máille), de Búrca succeeded his father as chieftain in 1375. Thomas died in 1402, and was succeeded by his son Walter mac Thomas de Búrca, 3rd Mac William Íochtar (d.1440). In total, Thomas had the following issue:

• 1 - Meyler, died 1384.
• 2 - David, died 1384.
• 3 - John, died 1384.
• 4 - Walter, died 1440.
• 5 - Edmond, died 1458.
• 6 - Thomas, died 1460.
• 7 - Richard, died 1473
• 8 - Meyler, died 1462.

From his son, Walter, descended almost all subsequent Mac William Iochtars and their successors.^[2]

From the Annals of the Four Masters:

• M1375.11. Sir Edmond Albanagh Mac William Burke died, after the victory of Penance: Thomas, his son, assumed the lordship after him.
• M1377.5. Rory O'Conor defeated Mac William Burke, and Melaghlin O'Kelly, Lord of Hy-Many, at Roscommon, where Richard Burke, the brother of Mac William, Donnell, the son of Cathal Oge O'Conor, Teige Oge, the son of Teige O'Kelly, O'Mainnin, Chief of Sodan, Mac Dowell Galloglagh, and many other persons not enumerated, were slain.
• M1380.3. Mac William Burke defeated Mac William Uachtrach (Richard Oge) at the town of Atha-leathann (Strade), where Mac Jordan de Exeter, Lord of Athleathan, and John de Exeter, were slain.
• M1384.13. Meyler, son of Sir William Burke, was killed by a fall. John and David, two other sons of Mac William Burke, died of the plague.
• M1385.8. Tireragh was burned by Mac William Burke; he afterwards went to Sligo, which was burned by him in like manner, together with South Carbury. But here battle was given to him, and Maidiuc Mael, one of the chiefs of his people, was slain; and hostages were afterwards forced from him.
• M1386.7. O'Conor Roe, with all the Connacians he could find to join him, went to assist Mac William Burke against Donnell, the son of Murtough O'Conor Sligo, and the Clann-Donough. They carried off great preys from Tir-Fiachrach Muaidhe. After this they proceeded to Clanrickard on a predatory excursion. O'Brien, with a great army, and Mac William of Clanrickard, came up with them; but O'Conor Roe turned round on them, and defeated them; and Conor, the son of Teige, son of Conor O'Brien, was slain in the conflict.
• M1386.11. A peace was made by the Connacians with one another after the war, and Mac William Burke went into the house of Mac William of Clanrickard, and ceded to him the lordship. Mac Feorais Bermingham went into his house in like manner.
• M1394.12. Mac William Burke, i e. Thomas, went into the King's house, and received great honour, and lordship, and chieftainship over the English of Connaught.
• M1395.16. Mac Jordan de Exeter was taken prisoner by the Clann-Mac-Jordan, and delivered up into the hands of Mac William Burke. An army was led by Donnell, the son of Murtough O'Conor, and the Irish of Lower Connaught, into Mac William's territory, in consequence of the capture of Mac Jordan; and Mac Jordan was liberated, and peace was ratified between the English and Irish of the province on this occasion.
• M1398.4. An army was led by Thomas Burke, Lord of the English of Connaught, and by O'Conor Roe and the sons of Cathal Oge, into Tirerrill, which they entirely plundered.
• M1398.20. Mac William Burke burned Sligo.
• M1401 (sic). Thomas, the son of Sir Edmond Albanagh Burke, i.e. Mac William, Lord of the English of Connaught, died, after the victory of penance. After the death of this Thomas Burke, two Mac Williams were made, namely, Ulick, the son of Richard Oge, who was elected the Mac William; and Walter, the son of Thomas, who was made another Mac William, but yielded submission to Mac William of Clanrickard for his seniority.^[3]

• House of Burgh, an Anglo-Norman and Hiberno-Norman dynasty founded in 1193