Phillip Parker King received a land grant in 1820 of 650 acres which he named Triangle Farm. No development appeared to have occurred until the 1940s. The Commonwealth acquired part of the land and a housing estate was established for employees of the St Marys Munitions Factory. Within this small estate there are 41 allotments, 33 with cottages and three open space areas. It is an early example of Radburn planning principles applied to housing sub-division designed by prominent Australian architect, Walter Bunning. The architect, a consultant to the Department of the Interior designed the houses to face the open space areas. During the late 1950s, the NSW Housing Commission acquired the majority of King’s grant and designed a new residential estate in a semi circular pattern. All of its streets were named after trees. This residential development coincided with a major industrial project at the St Marys Munitions Factory completed in 1957. The name – North St Marys – is indicative of the suburb’s northern location in relation to St Marys.