- Category: Populated Place
- Type: Village
- Latitude/Longitude: 51°46'50"N 3°40'38"W
- Eastings/Northings: 284388, 210440
- OS Grid: SN843104
- Mapcode Local: GBR Y9.Z2HD
- Mapcode Global: VH5G4.6HTS
Location and coordinates are for the approximate centre of Onllwyn within this administrative area.
Geographic features and populated places may cross administrative borders.