County Antrim, running from Belfast up along the Causeway Coast and the Glens, has a genuinely strong Irish sport horse and pony culture — Northern Ireland punches well above its size in producing capable, well-schooled ponies, and the Royal Ulster Agricultural Society's Balmoral Show, held near Belfast, is a major fixture drawing serious competitors from across the province. Good grazing runs from the fertile Lough Neagh shoreline up into the more rugged Glens.
Because Northern Ireland is geographically compact, a Antrim-based search realistically reaches most of the province within a couple of hours, and buyers regularly cross into County Down or further afield for the right pony. Sea crossings to and from Great Britain are a genuine consideration if you are buying from further afield — factor ferry or air freight costs into your budget if importing across the Irish Sea.