Before the seventeenth century, all members of this group of dogs were classified as “spaniels,” regardless of whether they were large or small, long-bodied or short, fast or slow, long-coated or short. Gradually, the size differences made an impression on hunters, and the larger dogs became used more so for springing game, while the smaller ones were used to hunt woodcock and other birds. The names Springer Spaniel, and Cocker or Woodcock Spaniel, naturally followed the skills of the developing breeds. The Kennel Club (of England) officially recognized them as distinct breeds in 1892. However, both types were found in the same litters even after their official separation by the English Kennel Club, with size being the dividing line between them. The Cocker and the Springer developed side by side, with the same heritage, coloring, hunting skills and general type. They were valued as great work and companion dogs during the 1900s. The larger dog developed as the English Cocker Spaniel, and the smaller dog developed into the American Cocker Spaniel.

During the late nineteenth century, two other distinct lines of Cockers developed. One involved dogs known as Field or Cocker Spaniels, which eventually branched out to become the Sussex, Field and Cocker Spaniels, with the latter being primarily black and weighing less than twenty-five pounds. The other line involved spaniels from the House of Marlborough, of which there were two types: a small, round-headed, short-nosed, red-and-white dog and a slightly larger dog with shorter ears and a longer muzzle. The Marlborough Cocker eventually became the English Toy Spaniel, but before they became a distinct breed they were crossed with smaller Cockers, and from those two lines came the American Cocker Spaniel known today.

The English Cocker Spaniel Club of America was founded in 1936, at which time the breed already was recognized as a variety of the Cocker Spaniel by action of the American Kennel Club Board of Directors, but not as a separate breed in its own right. The parent club’s aim was to discourage interbreeding of the English and American varieties of Cocker Spaniels. Fanciers of the English Cocker thought that this would be detrimental to their breed, and much controversy ensued. In 1940, the Canadian Kennel Club recognized the English Cocker Spaniel as a distinct breed, as did the American Kennel Club in 1946. Thereafter, reputable breeders recognized that this confusion in breed history was detrimental to the breed.