It is 45 kilometres (28 mi)west of the Sydney central business district, in the local government area of the City of Penrith.

The northern portion of St Marys/Dunheved is abundant with trade (especially automotive), manufacturing, waste processing, and storage centres, yet also contains a leagues club.

Other land grants in the area included those to Anna Josepha King in 1807 (Dunheved), Samuel Marsden (Mamre), and Mary Putland (Frogmore).

[10] The township formed part of a grant to Mary Putland (later married Sir Maurice O'Connell), the daughter of Governor William Bligh (former master of HMS Bounty, during the famous mutiny in 1789).

The St Marys & District Historical Society is open to the public on Wednesdays and Saturdays from 10 am to 2 pm in the Community Centre complex located on Mamre Road on the southern side of the Great Western Highway.

The northern half of St Marys, demarcated by the train line, is the site of numerous industrial and trade businesses, along with smaller specialist enterprises, most of which are situated alongside or branch from Glossop and Forrester roads.

The automotive industry has a major presence with wreckers, multiple kinds of workshops (paint, body, tyre and auto, brake and clutch, electrical, etc.

There are also some businesses along Railway Street adjacent to the southern side of train station, and a few along the Great Western Highway such as Aldi, Dominoes, a medical center, and the St Marys Band Club.

Station Plaza was a shopping centre which included a Coles Supermarket, around 16 specialty stores, and an undercover car park.

[46] The Wagon Wheel Hotel is another local pub/accommodation and derives its name from 'Bennet's Coach & Waggon Works', the business that was operated by brothers George T and James Jr. Bennet and which was situated near Queen Street from 1875 until its closure in 1920 (or 1858-1954 depending on the source).

[50] There is a small arts scene in St Marys, with sections of Queen Street being adorned in murals designed by independent artists, likely commissioned by the local council.

[51][52] Open-air concerts, holiday events, and family-friendly activities are often held in Coachmans park, around the middle of Queen Street.

[57] The Nepean Multicultural Access centre provides an assortment of community and social services, particularly for Culturally and Linguistically Diverse demographics.

The centre also holds scheduled activities including English conversation classes, indoor boules, sewing & needlework, pottery, painting, and gentle exercise sessions.