The original Yorkshire Terrier, known as the "Broken-Haired Scotch Terrier" was a 12-to-14 pound dog with wire hair whose intended purpose was the catching of rats and other vermin that lived in small spaces.
In 1870, the breed was renamed the Yorkshire Terrier, after the county of Yorkshire, England where the breed is believed to have originated. The father of the breed is considered to be Huddersfield Ben, who was born in 1865 and died in 1871 from a carriage accident, the inbred offspring of a mother and son. Huddersfield Ben was bred by Mr. W. Eastwood Huddersfield. A multiple champion, Huddersfield Ben set the foundation for what would develop into the modern Yorkie.
Based on registrations, Yorkshire Terriers became the #3 most popular dog breed in the United States in 2005 according to the American Kennel Club, trailing only the Labrador Retriever and the Golden Retriever.
Here is the link to a thread I posted before, according to the research I have done, the original yorkies, before they were the show quality small fries we know today, were actually larger to medium sized dogs! Here is the link to the thread, and there is a link to more info there on Xtra Large yorkies!
http://www.yorkietalk.com/forums/showthread.php?t=40548