Mountshannon County Clare
Irish: Baile Uí Bheann
'fort of (the) two peaks'According to one theory, the English name was borrowed from the demesne of Mount Shannon in Limerick, which is actually by the river Shannon.

Dunluce County Antrim
Irish: Dún Libhse
'palace' Dunluce Castle, now in ruins, is near the Giant's Causeway. The interpretation of the name, which is conjectural, derives from dún-lios, a combination of dún, 'fort', used adjectivally and lios, the word normally translated as 'ring-fort'. Perhaps the best rendering would be 'fortified residence'.

County Donegal
Irish: Dún na nGall
'fort of the foreigners'

The 'foreigners' were the Danes (the Vikings), who took possesion of a primitive fort here in the 10th century. The county took the name of the town.

From A Little Book of Irish Place Names by PW Joyce.