Definition of Londonderry
one of the Six Counties of Northern Ireland, formerly an administrative area. the chief town of Londonderry, a city and port on the River Foyle near its outlet on the north coast; population 89,900 (est. 2009). It was formerly called Derry, a name still used by many. In 1613 it was granted to the City of London for colonization and became known as Londonderry.