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. They were 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. They were in Co. Kerry in the south - west of the Munster Province.

De Lucy. Norman origins - 

Lucy. English origins. They came 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 (Dal gCais) the King of Thomond.

Ludlow. Originally de Lodelowe. English toponymic origins. They came 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 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 Luinigh / O Lunney. They were in Co. Donegal in the north - west of the Ulster Province. See also Lennon.

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. They were 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. They were 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. They were in the east of the Ulster Province.

O Lunne - Irish / Ua Lunney / Ua Luinigh / A Heremonian Ui Cobhthaigh Dal Cuinn "Northern" Ui Niaill Cenel nEogain Cenel Moen Sept / Family branch, who had their original territory to the west of Co. Derry at Magh Itha at Raphoe 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 in Central Ulster. See also - O Lennon. Ancestors - *88.Eogan the 1st King of Aileach (Cenel nEogain), *87.Niall of the Nine Hostages the 126th King of Tara / Ireland (Ui Niaill).

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

O Lunney - Irish / Ui Luinigh. A Sept / Family branch, who had their territory at Munterlooney in Co. Tyrone in Central Ulster.

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. A Heremonian Ui Cobhthaigh 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. 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. They 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.