Hay-on-Wye in Hay is a sub-office of Hereford, and therefore although in Wales has an English postal address, being part of the HR3 postcode. Hay-on-Wye is a Welsh community with a Town Council. Its boundary follows the English border/Dulas Brook from the River Wye southeastwards for just over a kilometre, turns south-west to a point just south of Oakfield house, thence north to Greenpit Farm and north westwards, enclosing the Hay Showground and meeting the National Park boundary near the B4350, Brecon Road. From this point, it follows the National Park boundary to the River Wye and the river back to
England–Wales border its residents at the time spoke Welsh. In the late 17th century under Charles II it was added to the Oxford circuit of the English Assizes, following which, according to the 1911 Encyclopædia Britannica, it gradually "came to be regarded as an English county". Under that interpretation, the boundary between England and Wales passed down the Rhymney valley, along Monmouthshire's western borders with Brecknockshire and Glamorgan, so including Newport, and other industrialised parts of what would now generally be considered to be South Wales, within England. The 1911 Encyclopædia Britannica unambiguously described the county as part of England, but noted