Letterkenny (Irish: Leitir Ceanainn) is the largest town in County Donegal, an Ulster county within the Republic of Ireland. It is located on the River Swilly. Despite its size, Letterkenny is not the County Town (administrative centre) of County Donegal. This function is fulfilled by Lifford, a small town to the east. Letterkenny dominates the economy of County Donegal, Ulster's largest county.[citation needed] The town is considered to be one of the fastest growing towns in all of Ireland. Letterkenny and the nearby City of Derry form the major economic core of North-West Ireland.