An Aussie is an Australian Shepherd. They were not actually developed in Australia. Here is some history that I pulled up.
The Australian Shepherd is known to have originated in the United States during the nineteenth century from a mixture of a number of different herding dogs, primarily from Europe, Latin America and to a lesser extent Australia. Throughout the 19th century, a large number of European herding dogs accompanied their owners to the East Coast of the United States. The East Coast climate was similar to the Spanish, Basque, and French areas many of the dogs had lived in previously, and the various breeds did well without having to make significant adjustments.
During the gold rush, the mass migration from East to West revealed that many of the European herding dogs were ill-suited to the hot, dry California climate. On the West Coast these newcomers were met by herding dogs from Latin America and Australia that had been brought to California to help in the gold harvest. European, Latin American and Australian dogs were interbred in an attempt to produce a competent herding dog that would fare well in a warm climate.
The result of this interbreeding, was a dog known today as the Australian Shepherd. The name Australian Shepherd, however, is a bit of mystery because the largest influx of Australian herding dogs did not take place until the 20th century, at which time the Australian Shepherd was already a well established type. Many of the Australian herding dogs on the West Coast of the United States were identified by a unique merle coloring, and it has been hypothesized that the term “Australian” may have simply been used to describe all dogs with merle markings.