The breed that a Chihuahua is mixed with is unknown. There are many ideas as to the origin of the breed, but there is no proof that any are true.
Some believe that the breed came from the South and Central American region and was developed through breeding of the Techichi dog. Others believe that the Chihuahua originated in China and was imported to the United States where it was bred with smaller native dogs. Still others believe that the breed was derived from the Fennec fox, native to South Africa.
Even with evidence that Chihuahuas have been around since ancient times, it is said to have originated in Mexico and is named for the state of Chihuahua located in that country.