Mac Diarmada (anglicised as McDermott or MacDermot), also spelled Mac Diarmata, is an Irish surname, and the surname of the ruling dynasty of Moylurg, a kingdom that existed in Connacht from the 10th to 16th centuries.
The progenitor of the family was Dermot mac Tadhg Mor, 7th King of Moylurg, who reigned from 1124 to 1159.
Later offshoot septs of the dynasty included the families of MacDermot Roe.
Moylurg ceased to exist as a kingdom in the late 16th century, though the senior line of the MacDermot's continued to live a sometime poverty-stricken and precarious existence despite land confiscations and the oppression of the Penal Laws.
During this era they were popularly accorded the title Prince of Coolavin;[citation needed] the current incumbent is Francis MacDermot,[citation needed] who succeeded by birthright to his father Rory MacDermot who died on 6 May 2021.