It borders four other parishes: Saint Ouen, Saint John, Saint Peter and Saint Lawrence. The parish and its eponymous church derive their name from a mediaeval monastery, probably destroyed during Viking raids some time between the 8th and 10th centuries. In 1042 William the Conqueror gave "Saint Mary of the Burnt Monastery" to the abbey of Cerisy.
Among the natural attractions of the parish is a feature known as the Devil's Hole (Lé Creux du Vis), a blowhole in the coastal cliff. The descent into the Devil's Hole used to be accessible to visitors and was a lucrative tourist attraction, but it has been closed off for decades. Following a shipwreck in 1851, when the ship's figurehead washed up in the Devil's Hole, a statue of a devil adapted from the figurehead was set up above the Hole. This wooden statue was replaced by a succession of modern versions in the 20th century.
Mourier Valley runs down the boundary between St Mary and St John. The stream formerly powered a number of mills despite the scant population of the area.
Crabbé is the location for pistol shooting.
Grève de Lecq lies on the border between St Mary and St Ouen. On the east side of the bay, in St Mary, lies Le Catel de Lecq, an ancient earthwork. In the bay, Le Moulin de Lecq, an old watermill was converted into a residence in 1929 and following the Second World War became a pub, while retaining the wheel and remnants of the gears.
The parish stands upon course-grained granite, 'of Saint Mary's type'. This granite was formerly quarried for building.
The parish is divided into vingtaines for administrative purposes as follows:
- Vingtaine du Sud
- Vingtaine du Nord
The parish forms one electoral district and elects one Deputy.
Saint Mary has the smallest population of all the parishes in Jersey, having only 1,591 residents in 2001.
- Historic Jersey, W S Ashworth, Jersey 1993 (no ISBN)