The name St Marys was first used when the "St Mary's" Post Office was opened on 1 October 1840. The township formed part of a grant to Mary Putland (later married Sir Maurice O'Connell), the daughter of Governor William Bligh (former master of , during the famous mutiny in 1789). Closer settlement of the area was made possible when in 1842 part of the O’Connell Estate was subdivided. St Marys has a long and rich industrial and agricultural history, including tanneries and munitions formerly operated by Australian Defence Industries.