<p><i>Chaetophractus villosus</i> is one of the 14 species of armadillos that inhabit Argentina. It belongs to the Magnorder Xenarthra; considered to represent the initial stock of mammals on the American continent. Only two previous genetic studies are known for this species. These postulated the Pampas region as its pre-expansion zone and the existence of a single ancestral haplotype. They also suggested that the species dispersed during the Pleistocene towards Patagonia from a single mitochondrial haplotype, the only one found in Patagonia, and that it recently colonized the area south of the Chubut River in the region. Here, we analyse the genetic diversity and structure of the species in Argentine Patagonia using a segment of the mitochondrial DNA control region and carried out a first approach to the study of historical demographic changes of large hairy armadillos. We found high values of genetic diversity, except for the population in Tierra del Fuego, and no population structuring. Bayesian population structure analyses identified three haplogroups, and the haplotype network presented a pattern suggesting an expansion event. In disagreement with previous works, our results showed that haplotype HC is the ancestral one but support a previous hypothesis suggesting that the Pampas Region represents the area from which individuals carrying haplotype HC colonised northern Patagonia. After that, around 750,000 years ago, a population expansion occurred, building the current mitochondrial diversity observed. Then, dispersal occurred south of the Chubut River about 200 years ago, and more recently, the species was introduced in Tierra del Fuego.</p>