Williamstown is a small South Australian village on the fringe of the Barossa Valley wine-growing region and the Adelaide Hills. It is 51 km north east of Adelaide and 16 km south-east of Gawler. Williamstown was originally known as Victoria Creek. The village was laid out in 1858 by Lewis Johnston, or Johnstone, on land he purchased in 1857, and named for his son.
The village has an elevation of 310m and an average rainfall of 680mm. It has a summer average temperature of 31°C with temperatures often reaching mid 40's, and a winter average temperature of 15°C, often dropping below freezing at night.
Williamstown is in the Barossa Council local government area, the state electoral district of Schubert and the federal Division of Mayo.