St John Parish is one of the 57 parishes of Cumberland County, New South Wales, a cadastral unit for use on land titles. It is named after St John's Cathedral in Parramatta, New South Wales which opened in 1803, on which the civil parish is roughly centred. The parish is shaped like a "T", with the northern part stretching from Toongabbie to the western shore of Homebush Bay. The southern end is at Prospect Creek near Yennora. Woodville Road and Parramatta Road form the boundaries to the south-east. The Old Prospect Road is part of the boundary in the west.