| Ciatlllait | A name of unknown origin. |
| Cillan | Variant of Ceallach: War; strife. |
| Cillian | Irish name meaning brightheaded one. |
| Cinneide | An Irish name meaning helmet head. |
| Cinneidid | Helmet head; helmed head. |
| Cinneidigh | Variant of Cinneidid: Helmeted; helmed head. |
| Clancey | Variant of Clancy: The red-haired soldier's son; ruddy warrior. |
| Clancy | A name meaning redhaired or warrior. |
| Cleonie | From the Greek Cleone daughter of a river god |
| Clodagh | Named after an Irish river. |
| Cluny | From the meadow |
| Coachuhhar | A rare indigenous name. |
| Coalan | A variant of the name Colin. |
| Cochlain | A name meaning little hood. |
| Coe | Diminutive of Cowan: Valley in a hill; twin. |
| Coghlan | A descendant of the captive. |
| Coilean | A young pup or a young dog. |
| Coilin | A small and young puppy dog. |
| Coillcumhann | From the narrow forest |
| CoireaIl | A name meaning a deep whirlpool. |
| Cole | Derives From Nicholas; From the dark town: Abbreviation of Nicholas people's victory.; Having dark features; having coal-black hair; From the name NICHOLAS; People's victory.; Prince of red roses; A swarthy woman; having coal-black hair |
| Colene | A maiden of noble stature. |
| Colhoun | Variant of Calhoun: Small forest. |
| Colla | An ancient Irish name whos meaning is lost in antiquety |
| Colleem | A variant of the name Colleen. |
| Colleen | An Irish word meaning young girl. |
| Collena | A variant of the name Colleen. |
| Collene | A variant of the name Colleen. |
| Colm | An Irish name meaning a dove. |
| Colmcilla | Dove of the church |
| Colmcille | Dove of the church |
| Columbo | Derived from the Latin columba |
| Coman | A name meaning noble or brave |
| Comdhan | Variant of Comhghan: Twin. |
| Comhghall | A Gaelic name meaning battle. |
| Comhghan | Born of a battle or conflict. |
| Comyn | Derived from a Scottish surname. |
| Comyna | A feminine form of the Comyn. |
| Conaire | Meaning hound of the sea king. |
| Conan | Little wolf or hound of war. |