
Drennan is a surname of Irish origin and is derived from the Gaelic Ó Draighnáin. first found in co Galway the surname has many anglisized forms inclueding Drennan, O'Drennan, Drennen, Drenan, Drenen, Thornton, etc. noted family members inclued;
William Drennan (1754 – 1820) United Irishmen