| Name | Locality | Local Authority | Administrative area |
| Yniscedwyn Road | Ystradgynlais | Powys / Powys | Powys / Powys |
| Yniscedwyn Road | Ystradgynlais | Powys / Powys | Powys / Powys |
| Ynisderw Road | Pontardawe | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynisydarren Road | Ystalyfera | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynisydarren Road | Ystalyfera | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Yns Y Gored | Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys Cadwyn | Glynneath | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys Close | Pontypridd | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynys Dawel | Solva | Sir Benfro / Pembrokeshire | Sir Benfro / Pembrokeshire |
| Ynys Fach Avenue | Resolven | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys Fawr Avenue | Resolven | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys Glyd Street | Gelligaer | Caerffili / Caerphilly | Caerffili / Caerphilly |
| Ynys Hir | Ynysybwl and Coed-y-Cwm | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynys Lane | Croesyceiliog | Tor-faen / Torfaen | Tor-faen / Torfaen |
| Ynys Las | Nelson | Caerffili / Caerphilly | Caerffili / Caerphilly |
| Ynys Nedd | Resolven | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys Newydd Road | Sketty | Abertawe / Swansea | Abertawe / Swansea |
| Ynys Street | Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys Street | Ynyshir | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynys Terrace | Pontypridd | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynys Y Coed | Llandaff | Caerdydd / Cardiff | Caerdydd / Cardiff |
| Ynys Y Wern | Cwmavon | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys-gyfeillon Road | Pontypridd | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynys-las | Llanelli Rural | Sir Gaerfyrddin / Carmarthenshire | Sir Gaerfyrddin / Carmarthenshire |
| Ynys-lee | Cwmavon | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys-lwyd Road | Aberaman | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynys-lwyd Street | Aberdare | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynys-meudwy Road | Pontardawe | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys-meudwy Road | Ystalyfera | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys-penllwch Road | Clydach | Abertawe / Swansea | Abertawe / Swansea |
| Ynys-penllwch Road | Clydach | Abertawe / Swansea | Abertawe / Swansea |
| Ynys-y-coed | Penmaen | Caerffili / Caerphilly | Caerffili / Caerphilly |
| Ynys-y-cwm Road | Llanelli Rural | Sir Gaerfyrddin / Carmarthenshire | Sir Gaerfyrddin / Carmarthenshire |
| Ynys-y-mond Road | Birchgrove | Abertawe / Swansea | Abertawe / Swansea |
| Ynys-y-mond Road | Clydach | Abertawe / Swansea | Abertawe / Swansea |
| Ynys-y-mond Road | Cilybebyll | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynys-yr-afon | Clyne and Melincourt | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynysallan Road | Birchgrove | Abertawe / Swansea | Abertawe / Swansea |
| Ynysangharad Road | Pontypridd | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynysbryn Close | Llantrisant | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynyscorrwg Road | Pontypridd | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynyscynon Road | Trealaw | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynyscynon Street | Cwmbach | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynysddu | Llanharan | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynysddu | Llantrisant | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynysfeio Avenue | Treherbert | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynysgau Street | Ystrad | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynyshir Road | Ynyshir | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynyshir Road | Ynyshir | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynyslas | Porthcawl | Pen-y-bont ar Ogwr / Bridgend | Pen-y-bont Ar Ogwr / Bridgend |
| Ynyslas Crescent | Glynneath | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynyslyn Road | Pontypridd | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynysmaerdy Terrace | Llanharan | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynysmeurig Road | Abercynon | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynysowen Fach | Merthyr Vale | Merthyr Tudful / Merthyr Tydfil | Merthyr Tudful / Merthyr Tydfil |
| Ynysteg | Ynysawdre | Pen-y-bont ar Ogwr / Bridgend | Pen-y-bont Ar Ogwr / Bridgend |
| Ynyswen | Llanelli Rural | Sir Gaerfyrddin / Carmarthenshire | Sir Gaerfyrddin / Carmarthenshire |
| Ynyswen | Llanelli Rural | Sir Gaerfyrddin / Carmarthenshire | Sir Gaerfyrddin / Carmarthenshire |
| Ynyswen Road | Treorchy | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynyswerdd | Penllergaer | Abertawe / Swansea | Abertawe / Swansea |
| Ynysybwl Road | Pontypridd | Rhondda Cynon Taf / Rhondda Cynon Taf | Rhondda Cynon Taf / Rhondda Cynon Taf |
| Ynysygerwn Avenue | Blaenhonddan | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynysygerwn Crescent | Blaenhonddan | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynysygored Road | Merthyr Vale | Merthyr Tudful / Merthyr Tydfil | Merthyr Tudful / Merthyr Tydfil |
| Ynysygwas Hill | Cwmavon | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynysymaerdy Road | Briton Ferry | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
| Ynysynos Avenue | Glynneath | Castell-nedd Port Talbot / Neath Port Talbot | Castell-nedd Port Talbot / Neath Port Talbot |
