| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 261 | Cinneidigh | Irish | Variant of Cinneidid: Helmeted; helmed head. | M | |
| 262 | Clancey | Irish | Variant of Clancy: The red-haired soldier's son; ruddy warrior. | M | |
| 263 | Clancy | Irish | The red-haired soldier's son; ruddy warrior. | M | |
| 264 | Cleary | Irish | Educated. | M | |
| 265 | Cluny | Irish | From the meadow. | M | |
| 266 | Coachuhhar | Irish | High desire. | M | |
| 267 | Cochlain | Irish | Hooded. | M | |
| 268 | Codell | Irish | Helpful. | M | |
| 269 | Codey | Irish | Helpful. | M | |
| 270 | Codie | Irish | Helpful. | M | |
| 271 | Cody | Irish | Helpful. | M | |
| 272 | Coe | Irish | Diminutive of Cowan: Valley in a hill; twin. | M | |
| 273 | Coghlan | Irish | Hooded. | M | |
| 274 | Coilean | Irish | Puppy. | M | |
| 275 | Coilin | Irish | Virile. | M | |
| 276 | Coillcumhann | Irish | From the narrow forest. | M | |
| 277 | Coinneach | Irish | Variant of Canice: Good-looking; handsome. | M | |
| 278 | CoireaIl | Irish | Lordly. | M | |
| 279 | Coleman | Irish | Dove. | M | |
| 280 | Colhoun | Irish | Variant of Calhoun: Small forest. | M | |