O Luby. Originally O Looby - Irish / Ua Lubaigh / lubach (cunning).  A Sept / Family branch, who had their territory in Co. Tipperary in the north - east of the Munster Province. O Looby still used in Northern Leinster.

Lucas / Luke. Originally anglicized as Luiseid. Anglo - Norman origins in Ireland in the 14th Century AD and in the 17th Century AD they were in Co. Waterford in the south - east of the Munster Province.  After the Oliver Cromwell Invasion they spread also into Leinster Province and the Ulster Province.

Mac Lucas. Highland Scottish origins -

O Lucey. Original Irish / Mheic Cluasaigh / Ua Luasaigh now used. A Sept / Family branch, who had their territory in Co. Cork in Southern Munster.

Lucid. May be a derivative of Lucas / Luiseid, which see who were in Co. Kerry in the south - west of the Munster Province.

De Lucy. Norman origins - 

Lucy. English origins from Oxfordshire and were in Co. Fermanagh in the south - west of the Ulster Province.

O Ludden. Used as a variant for O Lydon, which see, in Co. Galway and Co. Mayo in the west of Southern Connacht.

O Luddy - Irish / Ua Loidigh. Used as a variant for O Liddy, which see, in the north of Co. Cork in Southern Munster. Ancestor:*91.Cas  the King of Thomond. (Dal gCais).

Ludlow. Originally de Lodelowe. English toponymic origins from Shropshire and were in Ireland in the 14th Century AD, but did not settle permanently until the 17th Century AD. They were initially in Co. Meath and Co. Louth in the east of Northern Leinster and nearby in Co. Dublin in the north - east of Southern Leinster and were also in Co. Cork in Southern Munster and the Ulster Province.

Luke. Scottish origins. Used as a synonym for Mac Lucas, which see.

Luff. A derivation of Mac Loughlin. The Mac was dropped first, then Lin dropped, leaving just Lough sounded in that region as rough or tough / Luff. This particular Mac Loughlin Sept / Family branch has now been there for over 50 years on Jersey and Norfolk.

O Lughaidh / Irish / Ua Leithrinn. Heremonian Dal Cuinn Colla Da Crioch Sept / Family branch.Ancestors: *86.Cairbre Liffeachair the 117th King of Tara / Ireland.  87.Eochy / Echu Doimhlen, 88.Murray / Muireadach Colla Da Crioch / Focrith - of the Two Countries, 89.Rochadh, 87.Deach Dorn, 91,Fiach / Feig, whose brother, 91.Labhradh is the direct male ancestor of the O Laurys / Ui Laury, and another brother, 91.Brian is the direct male line ancestor of the O Briens / Ui Briain of Arcaill, 89.Criffan / Crimthann Liath - of the Grey Hair is the ancestor of the O Griffins / Ui Criomhthainne of Ulster who was the King of Orgialla who was aged when St. Patrick came to Ireland for the second time. He had 5 sons, 90.Fergus Ceanfhada - a Learned Man,  the direct male line ancestor of the O Kennedys / Ui Ceanatta who also assisted *91.Leary / Laoghaire the 128th King of Ireland, 89.Conall Corc the Heberian King of Munster, Daire the Prince of Ulster, St. Patrick, St. Benignus and St. Carioch to review the records and the Brehon Laws of the kingdom.  90.Eochy / Eochaidh, 90.Lewy / Lughaidh the direct male line ancestor of the O Lughaidh / Ui Leithrinn Sept, 90.Murray / Muireadach the ancestor of the Mac Brocks and 90.Aodh / Eochaidh the ancestor of the O Slevins.

O Luigheach / Irish / Ua Luigheach. A Sept / Family branch, who had their territory in Co. Tipperary in Ormond / Aur Mhumhain in the north - east of Northern Munster.

O Luinn - Irish / Ua Luinin. A Sept / Family branch, who had their territory in Co. Fermanagh in the south - west of the Ulster Province.

O Lumley - Irish / Ua Lomthaile.A Sept / Family branch, who had their territory in Co. Cork in Southern Munster.

Lumley / de Lumley. English locative origins -

O Lundergan. See O Londrigan.

Lundon. Used as a variant for London, which see.

Lundy. English origins in Co. Derry in the north - east of the Ulster Province. Robert Lundy was the Mayor of Derry during the siege of Derry by James 11.

Lundy / de La Lounde. Norman origins in Co. Kilkenny in the south - west of Southern Leinster and nearby in Co. Tipperary in the north - east of the Munster Province.

Lunn. English origins in the east of the Ulster Province.

O Lunneen. Used as a variant for O Linneen, which see.

O Lunney or O Lunne - Irish / Ui Luinigh. Heremonian Dal Cuinn Cenel nEogain Cenel Moen Sept / Family branch, who had their original territory to the west of Co. Derry at Magh Itha at Raphoe / Munterlooney in Co. Donegal in the north - west of the Ulster Province and nearby in Co. Tyrone in the west of Ulster Province where they were Chiefs Ancestors: *90.Niall of the Nine Hostages the 126th King of Tara / Ireland (Ui Niaill), 91.Eogan the 1st King of Aileach (Cenel nEogain), 92.Murray / Muireadach the 2nd King of Aileach, 93.Maein, See also O Lennon.

Mac Lure. See Mac Clure.

Mac Lurg. See Mac Clurg.

Mac Lurigan. Used as a variant for Longergan, which see, in the west of Co. Clare in the north - west of the Munster Province.

O Lurkan or O Lurkayne. Heremonian Dal Cuinn Colla Da Crioch Airthir Ui Niallain Clann Cernaich Sept / Family branch, who had their territory at Oneilland East and West in Co. Armagh in the south - east of the Ulster Province and the adjacent country in Co. Monaghan in Southern Ulster where they were  the Chiefs of Farney and West Ui Breasail. Especially see O Larkin.

Lush. A derivation akin to Usher and not connected to Lusk.

Lusk - Irish toponymic. This was an original village in Co. Dublin in the north - east of Southern Leinster. They are now found in the north - east of the Ulster Province.

Lusty. See Losty.

Luther. See Lowther.

Lutheran. See Loughran.

Luttrell or Lutterell or Lutterville / Le Lutrel (the Otter) French origins who were one of the important families in The English Pale surrounding Dublin in Co. Dublin in the north - east of Southern Leinster since the 13th Century AD.