- Cairgin
- Three miles south of Londonderry.
- Carrthach River
- River Carra, near Dunkerrin Mountains.
- Ceanntaile
- Kinsale.
- Ceiscorainn
- Co. Sligo.
- Cill Dolun
- Killaloe, Co. Clare.
- Cliodna's Wave
- At Glandore, Co. Cork.
- Cluantarbh
- Clontarf.
- Cnoc Aine
- Co. Limerick.
- Cnoc-an-Air
- Co. Kerry.
- Cnoc na righ
- Co. Sligo.