district in southwestern Scotland (Medieval Latin Gallovidia), equivalent to Welsh Gallwyddel, Irish Gallgaidhil, literally "foreign Gaels," containing the Gal- element also common in Irish place-names (Irish Gaelic gall) and meaning there "a stranger, a foreigner," especially an Englishman. Related: Gallovidian, which is from the Latin form of the name. The adjective Galwegian is on analogy of Norwegian.
<a href="https://www.etymonline.com/word/Donegal">Etymology of Donegal by etymonline</a>
Harper, D. (n.d.). Etymology of Donegal. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/Donegal