The ancient principality of Tír Eoghain is in Londonderry .
The ancient principality of Tír Eoghain , the inheritance of the O'Neills , included the whole of the present counties of Tyrone and Londonderry , and the four baronies of West Inishowen , East Inishowen , Raphoe North and Raphoe South in County Donegal .
County Tyrone