O Delargy - Irish / Ua Duibhlearga - learg / plain or slope. A Sept / Family branch, who had their original territory in Co. Mayo in the mid - west of the Connacht Province and later migrated to Co. Antrim in the north - east of the Ulster Province before the mid - 17th Century AD.

O Deloughery - Irish / Ua Dubhluachra - dubh / black. A Sept / Family branch, who had their territory in Co. Cork in Desmond / Des Mhumhain / Southern Munster. 9 different Spellings were used there including Deloorey and Dilloughery and a synonym, Dilworth.

O Dempsey or O Dempsie - Irish / Ua Diomasaigh - diomasach / proud man. A Heremonian Ui Laoghaire Cu Corb Clann Maellugra Clanmalier Sept / Family branch, who had their territory in Co. Laois and Co. Offaly in the north - west of Southern Leinster. They are originally descended from *60.Leary / Laoghaire "Lorc" who in 593 BC was the Heremonian 68th King of Tara / Ireland who was a son of the *59.Ugaine "Mor" - the Great the 66th King of Tara / Ireland. In 120 - 123 AD his descendant, *88.Cahir / Cathair "Mor" was the 109th Heremonian Cu Corb King of Tara / Ireland who was killed at the Battle of Moigh Acha and his son 89.Fiacha "Ba hAiccid" was made lame. Another son, *89.Ros "Failge" is the ancestor of the Ui Failge / Ui Conchobair Failghe / O Connor "Faly," Ui Riacain / O Dunnes, and the O Dempseys from the Clann Maellugra. Another son, 89.Criffin / Crimthann is the ancestor of the Ui Crimthainn Ain / O Duffs. Another son, 89.Daire "Barrach" is the ancestor of the Ui Bairrche / Mac Gormans. Another son 89.Ailill "Cetach" is the ancestor of the Ui Cheithig / Crich na Cetach Sept. Another son, 89.Bressal "Enechglas" is the ancestor of the Ui Enechglais Sept / O Fearys. The O Dempseys were Kings and Chiefs in their territory at Clanmalier between Co. Laois and Co. Offaly in the west of Southern Leinster where they were strong Irish Patriots. In the 12th Century AD O Dempsey actually defeated Strongbow / Richard de Clare in battle during the Anglo - Norman Invasion. Because of their geographic situation to The English Pale they also were to eventually succumb and were appointed English Viscounts and Barons. During the Elizabethan Wars they were to side with Elizabeth 1st and later James 1st to hold onto their territory there and because of this Terence Dempsey was appointed the English Viscount Clanmalier. In 1689 AD their Irish Chiefs were situated at Geashill in Co. Offaly on both sides of the River Barrow, and seeing a light at the end of the tunnel for Ireland they sided with James 11 the Stuart Catholic English King and lost their territory there to the English anyway who gave it over to Lord Digby who renamed their castle after himself. They were also in Co. Kildare in Central Southern Leinster and  always came under intense pressure from the English who were always trying to expand the boundaries of The English Pale around Dublin in Co. Dublin to attack the surrounding Irish Septs. Maximilian O Dempsey, who was the English Lord Viscount Clanmalier, who died on 30. 11. 1690 AD, was to be the last of their Irish aristocratic male line who were to be the Princes of Offaly. Ancestors - *60.Leary / Laoghaire "Lorc" the 68th King of Tara / Ireland (Ui Laoghaire), *84.Cu "Corb."

Dempster. Manx origins / judge. They were in Co. Down in the south - east of the Ulster Province. Also used as a synonym for Dempsey, which see.

Denieffe. English origins. They were in Co. Kilkenny in the south - west of Southern Leinster since the 18th Century AD. Sometimes shortened to Neef.

Denn. They were in Co. Waterford in the south - east of Ormond / Eastern Munster and nearby in Co. Kilkenny / Ossory in the south - west of Southern Leinster. Also see de Denne under Deane.

O Dennan or O Dennany or O Denneny - Irish / Ua Doineannaigh - doineannach / tempestuous. A Sept / Family branch, who had their territory in Co. Cavan in Southern Ulster and the surrounding Counties.

                                                                                 +On to O Dennehy - Fitz Dermot