North St Marys is a suburb in western Sydney, in the state of New South Wales Australia.

North St Marys is located 47 kilometres west of the Sydney central business district, in the local government area of the City of Penrith.

Prior to European settlement, what is now North St Marys was home to the Gomerrigal-Tongarra people who spoke the Darug language.

At a local government level, North St Marys is part of the east ward of Penrith City Council, represented by Prue Car, Greg Davies, Maurice Girotto, Jackie Greenow and Tricia Hitchen.

At the state level, it is part of the Electoral district of Londonderry, represented by Prue Car of the Australian Labor Party.