Thornlie is a large residential suburb of Perth, the capital city of Western Australia, located 15 kilometres south-east of the city's central business district. It is a part of the City of Gosnells local government area. The Canning River runs through the northern side of the suburb. Since the 1950s the suburb has developed in approximately five stages; north-east Thornlie, south Thornlie, Crestwood, Castle Glen and Forest Lakes.