Tomlagh is an ancient Irish district in what is now southern County Londonderry

County Londonderry

The place name Derry is an anglicisation of the old Irish Daire meaning oak-grove or oak-wood. As with the city, its name is subject to the Derry/Londonderry name dispute, with the form Derry preferred by nationalists and Londonderry preferred by unionists...

, Northern Ireland

Northern Ireland

Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...

. Killetra along with the ancient districts of Clandonnell

Clandonnell

Clandonnell is an ancient Irish district in what is now southern County Londonderry, Northern Ireland. Clandonnell along with the ancient districts of Glenconkeyne, Killetra, and Tomlagh, comprised the former barony of Loughinsholin, with Clandonnell forming the northern part reaching as far south...

, Glenconkeyne

Glenconkeyne

Glenconkeyne is an ancient Irish district in what is now southern County Londonderry, Northern Ireland. Glenconkeyne formed the western portion of the former barony of Loughinsholin, with the ancient districts of Clandonnell, Killetra, and Tomlagh comprising the rest...

, and Killetra

Killetra

Killetra is an ancient Irish district in what is now southern County Londonderry, Northern Ireland. Killetra along with the ancient districts of Clandonnell, Glenconkeyne, and Tomlagh, comprised the former barony of Loughinsholin, with Killetra reaching from the present-day town of Magherafelt to...

, comprised the former barony of Loughinsholin. Tomlagh is stated as forming a four or five mile wide district running from Portglenone

Portglenone

Portglenone is a village in County Antrim, Northern Ireland. It lies 8.5 miles west of Ballymena. It had a population of 2,900 in the 2001 Census...

 to Lough Beg

Lough Beg

Lough Beg is a small freshwater lake north of Lough Neagh in Northern Ireland. The lake is located on the border between County Londonderry and County Antrim....

. The townland of Annaghmore, near Castledawson

Castledawson

Castledawson is a village in County Londonderry, Northern Ireland. It is mostly within the townland of Shanemullagh , about four miles from the north-western shore of Lough Neagh, and close to the market town of Magherafelt...

is mentioned in Bodley's map from 1609 as lying within Tomlagh.