Dog expert, Stonehenge (J. H. Walsh), writing in 1887, shows his contempt for all things not inherently British with his refusal to believe that the Irish Terrier was a distinct breed from the "old Scotch terrier." But the differences were distinct. The truth might be that the raiding Irish could have introduced the prototype to Scotland many centuries ago. Or perhaps the Celts, who conquered both Scotland and Ireland four centuries before Christ, brought the archetypical terrier with them, and differences developed after that.

Whatever the early history, by the middle of the 1800s, the Irish Terrier, jacketed in black/tan and brindle as well as the more desirable red, was a common sight. During these years, many of this breed were seen with cropped ears, a sure sign they were used for dog-fighting. The Irish Terrier's punishing jaws bode the end of many an Irish rat. But despite the instincts to destroy vermin, he could be a soft-mouthed retriever and often wore two hats: ratter and hunter. There was still variation in size and type at the breed's debut at an Irish show in 1875. Out of the 50 dogs that strutted the ring, entries included some in the under nine-pound division and one that was over 30 pounds; a pure white entry competed against many that would have passed for Cairns. These differences existed despite the rule that the dogs must have a pedigree to enter. Many had notes attached reading, "Breeding information available at such-and-such an address." The winner, "Boxer" by name, was brazenly labeled as "Bred by owner, pedigree unknown!'' This mass confusion prompted the formation of a strong breed club still in existence today.