Chadwell St Mary is an area of the unitary authority of Thurrock in Essex, England. It is one of the traditional (Church of England) parishes in Thurrock and a former civil parish. Grays is 2 miles (3.2Â km) to the west and 1 mile (1.6Â km) to the south is Tilbury. The area is sometimes referred to simply as Chadwell, particularly before the 19th century.