| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 141 | Casey | Celtic | Brave. | M | |
| 142 | Cassivellaunus | Celtic | From Arthurian legend. | M | |
| 143 | Caswallan | Celtic | From Arthurian legend. | M | |
| 144 | Cathair | Celtic | Fighter. | M | |
| 145 | Cathal | Celtic | Strong in battle. | M | |
| 146 | Cathaoir | Celtic | Fighter. | M | |
| 147 | Cedric | Celtic | Cbief. | M | |
| 148 | Celyddon | Celtic | Mythical father of Culhwch. | M | |
| 149 | Chad | Celtic | Defence. | M | |
| 150 | Clust | Celtic | Mythical son of Clustfeinad. | M | |
| 151 | Clustfeinad | Celtic | Mythical father of Clust. | M | |
| 152 | Cocidius | Celtic | Mythical hunter god. | M | |
| 153 | Coinneach | Celtic | Handsome. | M | |
| 154 | Con | Celtic | Wise. | M | |
| 155 | Conal | Celtic | High; mighty. | M | |
| 156 | Conall | Celtic | Strong in battle High; mighty. | M | |
| 157 | Conall Cernach | Celtic | Mythical Ulster chieftain. | M | |
| 158 | Conan | Celtic | High, wise. Introduced into Britain after the Norman Conquest. Famous bearers: Sir Arthur Conan Doyle, creator of the detective Sherlock Holmes; a number of counts and dukes of Brittany bore the name Conan. | M | |
| 159 | Conant | Celtic | Wise. | M | |
| 160 | Conchobar | Celtic | Mythical hero. | M | |