O Duane or O Devane - Irish / Ua Diubhain. An Erenagh Sept / Family branch, who had their territory at Killursa in Co. Galway in Southern Connacht.

O Duanny. Used as a variant for O Devany, which see.

O Ducey or O Doocey - Irish / Ua Dubhghusa - dubh / black - gus / action. A Sept / Family branch, who had their territory in Ormond / Aur Mhumhain / North Eastern Munster.

Duck. Used as a synonym for Lohan, which see / lacha - duck.

O Duddy. Especially see - O Dowd.

Dudgeon. Used as a variant for Dodge, which see. They were in the west of the Ulster Province in the late 16th Century AD and then in Co. Monaghan in Southern Ulster.

O Dudley - Irish / Ua Dubhdaleithe - da / two - leithe / sides. A Sept / Family branch, who had their territory in Co. Cork in Desmond / Des Mhumhain / Southern Munster where their name was also anglicized to O Dowdall, which see

O Dudley. A Heremonian Ui Laoghaire Ui Lughaidh Cu Corb Sept / Family branch. Anglicized from O Dunlaing. Especially see - O Dowling.

Dudley. English toponymic origins -

O Duff or O Duffy or Duffe - Irish / Ui Duibh. An Irian Laeghis Cenel Crimthainn / Ui Crimthainn Ain Sept / Family branch, who were the  Kings of Creamhthainn (Maryborough.) Kinsmen to O Devoy / O Deevy / Ui Duibhuidhe, O Hourihan / Ui hIndreadhain who had their territory at Ballyduff in Stradbally in Co. Laois in the mid - north - west of Southern Leinster. Ancestor - *37.Ir (Irians).

O Duff or O Duffe. Actually O Duffin - Irish / Ua Dubh - black. A Sept / Family branch, who had their territory in Co. Laois in the mid - north - west of Southern Leinster where they were Chiefs.

Mac Duff / Mheic Dubh. Actually Mac Elduff, which see, who were in Co. Tyrone in Central Ulster.

Mac Duff. Highland Scottish origins. They were in the Ulster Province.

O Dufferley. Used as a variant for Doorley, which see, in Co. Roscommon in the east of the Connacht Province.

O Dufficey - Irish / Ua Dubhghusa. A Sept / Family branch, who had their territory in the Connacht Province. See also O Ducey.

O Duffin - Irish - originally Ua Duibhghinn. Ua Duibhinn now used. A Sept / Family branch, who had their territory in Co. Waterford in the south - east of Ormond / Aur Mhumhain / North Eastern Munster. Now also found in the east of the Ulster Province and nearby in Co. Louth in the north - east of Northern Leinster.

O Duffy - Irish / Ua Dhubthaigh / dubhthach / dark one. A Heremonian Ui Cobhthaigh Dal Cuinn Colla da Crioch Sept / Family branch, who had Septs in Co. Galway, Co. Mayo and Co. Roscommon in the Connacht Province and Co Donegal in the north - west of the Ulster Province. They were also Chiefs in Co. Monaghan in Southern Ulster where Charles Gavan Duffy who was a founder of the Young Irelanders and later became the Premier of Victoria in Australia and his son, Gavan Duffy originated. They also built Boyle Abbey in the 12th Century AD in Co. Meath in the south - east of Northern Leinster. See also - Duhig. Ancestors - *85.Murray "Colla da Crioch" "Focrith" - of the Two Countries, *84.Eochy / Echu "Doimhlen, *83.Cairbre "Liffeachair" the 116th King of Tara / Ireland.

O Dugan. A Sept / Family branch, who had their territory in Co. Wexford in the south - east of Southern Leinster where they were Chiefs. They were also nearby in Co. Cork in Desmond / Southern Munster.

O Duggan or O Dugan or O Doogan or O Deegan - Irish / Ua Dubhgain / Duibhgin. A Heberian Dal gCais Sept / Family branch, who were the Dalcassian Chiefs of Muintir Conlochta who had their territory around Tomangraney in the Barony of Tullagh in Co. Clare in the north - west of Thomond / Tuaiscert Mhumhain / Northern Munster. Ancestor - *91.Cas (Dal gCais) the King of Thomond.

O Duggan or O Dugan - Irish / Ua Dubhgain. A Fir Maighe Sept / Family branch, who had their territory at Caher Duggan at Fermoy / Fir Maighe in the north of Co. Cork in Desmond / Des Mhumhain / Southern Munster. They survived until the 13th Century AD when the Anglo - Norman English finally took away their territory also.

O Duggan or O Dugan or O Doogan - Irish / Ua Dubhgain. A Heremonian Ui Cobhthaigh Dal Cuinn Ui Maine Sept / Family branch, who had their territory in Co. Mayo, and nearby in the east of Co. Galway and in the south of Co. Roscommon in the Connacht Province. Ancestors - *86.Maine "Mor" (Ui Maine), *85.Murray / Muiredach "Tireach" the 122nd King of Tara / Ireland, *80.Conn of the Hundred Battles the 110th King of Tara / Ireland (Dal Cuinn).

Duglas -