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 Skenfrith (in Wales), towards Monmouth, looping eastwards to include the town itself and a surrounding area within Wales. At Redbrook, the boundary again reaches the Wye, and follows the river southwards, past Tintern and Chepstow on the Welsh side, to its confluence with the Severn at the Severn Bridge. The boundary then continues down the Severn estuary towards the Bristol Channel, with the small island of Flat Holm being administered as part of Wales and the neighbouring island of Steep Holm as part of England. The boundary passes between Flintshire, Wrexham County Borough, Powys, and Monmouthshire in Wales and Cheshire