| PO Number | Town / Place name | Code |
|---|---|---|
| 100 | Carn | |
| Carrickmore | ||
| 101 | Carnew | |
| Carrickmines | ||
| 102 | Carrickfergus | |
| 103 | Carrickmacross | |
| 104 | Carrick-on-Shannon | |
| 105 | Carrick-on-Suir | |
| 106 | Cashel | |
| 107 | Castlebar | |
| 108 | Castlebellingham | |
| 109 | Castlegregory | |
| 110 | Castleblakeney | |
| 111 | Castleblayney | |
| 112 | Castlecomer | |
| Castleconnell | ||
| 113 | Castleconnell | |
| 114 | Castledawson | |
| 115 | Castlederg | |
| 116 | Castledermot | |
| Castleknock | ||
| 117 | Castlefin | |
| 118 | Castlemartyr | |
| 119 | Vacant 1844 - 1906 | |
| 120 | Castlepollard | |
| 121 | Castlerea | |
| 122 | Castlerown | |
| Castletown Bere | ||
| 123 | Castletown Devlin | |
| Castletown Mullingar | ||
| Castletown Geoghegan | ||
| 124 | Castletownroche | |
| 125 | Castlewellan | |
| 126 | Cavan | |
| 127 | Celbridge | |
| 128 | Charlevlle | |
| 129 | Church Hill | |
| Clifden | ||
| 130 | Clane | |
| 131 | Clare | |
| Clanabogan | ||
| 132 | Clare | |
| Claremorris | ||
| 133 | Clashmore | |
| Clara | ||
| 134 | Clifden | |
| Clandeboye | ||
| 135 | Cloghan | |
| 136 | Clogheen | |
| 137 | Clogher | |
| Clonee | ||
| 138 | Cloghnakilty | |
| Clonakilty | ||
| 139 | Clonard | |
| Cleggan | ||
| 140 | Clonee | |
| Clonelly | ||
| 141 | Clones | |
| 142 | Clonmel | |
| 143 | Clough, Down | |
| Clough, Newry | ||
| 144 | Cloughjordan | |
| Consilla | ||
| 145 | Cloyne | |
| Cloughjordan | ||
| 146 | Coachford | |
| Clonbur | ||
| 147 | Coleisland | |
| 148 | Colehill | |
| Clogher | ||
| 149 | Coleraine | |
| 150 | Collon | |
| Collooney | ||
| 151 | Collooney | |
| Coachford | ||
| 152 | Cong | |
| Comber | ||
| 153 | Comber | |
| Coole | ||
| 154 | Cookstown | |
| 155 | Cootehill | |
| 156 | Cork | |
| 157 | Cove | |
| Queenstown | ||
| 158 | Carrigart | |
| Courtmachsherry | ||
| 159 | Craughwell | |
| Corofin | ||
| 160 | Creeslough | |
| Craughwell | ||
| 161 | Crookstown | |
| Crossgar | ||
| 162 | Crossakeil | |
| 163 | Crossdoney | |
| 164 | Crossmolina | |
| 165 | Croome | |
| Croom | ||
| 166 | Crumlin | |
| Crossmolina | ||
| 167 | Corofin | |
| Cullybackey | ||
| 168 | Cushendall | |
| 169 | Dartrey | |
| 170 | Dangan | |
| Draperstown | ||
| 171 | Delgany | |
| 172 | Derry | |
| 173 | Dervock | |
| 174 | Dingle | |
| 175 | Donaghadee | |
| Donaghmore | ||
| 176 | Donegal | |
| 177 | Doneraile | |
| Donabate | ||
| 178 | Down | |
| Downpatrick | ||
| 179 | Drogheda | |
| 180 | Dromond | |
| Dromore, Tyrone | ||
| 181 | Dromore, Down | |
| Dromond | ||
| 182 | Dromore, West | |
| Dromore, Down | ||
| 183 | Drumcree | |
| Drumsna | ||
| 184 | Drumsna | |
| Drumcondra | ||
| 185 | Draperstown | |
| 186 | Dublin | |
| 187 | Dundalk | |
| 188 | Dunfanghy | |
| 189 | Dundrum | |
| 190 | Dundrum | |
| Dublin and Belfast R.P.O. | ||
| Dunkineely | ||
| 191 | Drumkeerin | |
| 192 | Drumora | |
| Dungloe, Don | ||
| Dunmore, Tuam | ||
| 193 | Dungannon | |
| 194 | Dungarvan | |
| 195 | Dungiven | |
| Dunkettle Station | ||
| Glanmire | ||
| 196 | Dunlavin | |
| Dunadry | ||
| 197 | Dunleer | |
| 198 | Dungloe | |
| 199 | Dunmurry |