|OS grid reference|
|• Cardiff||84.1 mi (135.3 km)|
|• London||213.2 mi (343.1 km)|
|Sovereign state||United Kingdom|
|Fire||Mid and West Wales|
|Senedd Cymru – Welsh Parliament|
Walwyn's Castle (Welsh: Castell Gwalchmai) is a village, parish and community in the county of Pembrokeshire, Wales, and is 84 miles (135 km) from Cardiff and 213 miles (343 km) from London. In 2011 the community's population was 361. 
In his 12th century Gesta Regum Anglorum, William of Malmesbury claimed that the grave of Gawain (Latin: Walwen, Welsh: Gwalchmai) was found here around the end of the 11th century and that the castle mound covers the site.
A castle was built within an Iron Age Hill fort by the Normans. There is an historic rath overlooking Walwyn's Castle. A geophysical survey was carried out in 2011.
Walwyn's Castle was in the ancient hundred of Roose with its origins in the pre-Norman cantref of Rhôs. This and several other parishes fell within the mediaeval Barony of Walwyn's Castle, the caput of the Marcher Lord.
The earliest-known reference to Walwyn's Castle Church was 1291. The church was rebuilt around 1869 to 1878. Today the Church is in good repair with services held there every Sunday.
The village school closed in the late 1950s, converted to a village hall, and substantially renovated in 2004.
- Gwalchmai Bangor University Placenames Unit (Canolfan Bedwyr); accessed 9 May 2014
- Google Maps (Map). Google.
- "Pembrokeshire Town and Community Councils: Walwyns Castle". Retrieved 27 March 2020.
- Welsh Government website; 2011 Census Returns and stats; accessed 9 May 2014
- Gesta Regum, William Stubbs, 1889, vol. 2, p. 89
- "GENUKI: Walwyn's Castle". Retrieved 9 March 2016.
- "Dyfed Archaeology: Hoaten to Hasguard". Retrieved 25 March 2020.
- "GENUKI Parish Map 162". Retrieved 27 March 2020.
- Media related to Walwyn's Castle at Wikimedia Commons