Passage: Located on the south central margin of the province, it is adjacent to the eastern border of Guangxi. The county is bordered to the north by Shaoyang County, to the east by Lengshuitan District, to the south by Lingling District, Quanzhou County of Guangxi, to the west and the northwest by Xinning County. Dong'an County covers 2,204 km2 (851 sq mi), as of 2015, It had a registered population of 643,179. The county has 13 towns and 2 townships under its jurisdiction, the county seat is Baiyashi (白牙市镇).Dong'an County is the source place of Dong'an Chicken (东安子鸡), which is one of well-known  Hunan foods.

Question: WHat is the population of Dong'an county?
643,179