There are 2 potential origins of the Yancy surname. The first is the anglicised form of the Dutch surname Janse or Janze (pronounced Yancey). The surname Janse is of patronymic origin, being derived from the first name of the father of the initial bearer. In the instance of Janse, it is the pet form of the first name Jan, which is itself a shortened form of Johann or John. Exact origin of the Bretan surname Janze is not exactly known, although it too is likely derived from John.
Both Janse and Janze were found in France in the provinces of Nord (where a form of Dutch is spoken) and Brittany (where Breton is spoken) respectively.
The Civil War saw the family split, with the dropping of the "e" from the last name. While there is no concrete documentation to this, it is believed those faithful to the Union kept the "e", while those who supported the Confederacy did not.