Glen Forrest is a suburb within the Shire of Mundaring, south of John Forrest National Park, west of Mahogany Creek, east of Darlington, and north of the Helena River. Its northern boundary is determined by the Great Eastern Highway.
Originally known as Smiths Mill after a prominent founder citizen, it is currently named after the first Premier of Western Australia, Sir John Forrest.
The suburb is bisected by a disused railway track - the original route of the Eastern Railway - which is now known as the Railway Reserve Heritage Trail, and Nyaania Creek.
It has a number of significant conservation reserves including the Glen Forrest Super Block which is adjacent to Ryecroft Road ( the main connecting road to Darlington). It also has the only road that runs through to the Helena River valley from the suburbs between Mundaring Weir and the Helena Valley locations.
The major extractive industries were early forestry, and the Stathams brickworks, which had its own siding, just east of the railway yard. The brickworks was located on a patch of white clay, that is now a park and recreation area.
It has two commercial areas - one adjacent to, and just north of the former railway station site, and the other at the intersection of Hardey Road and Great Eastern Highway.
Like Darlington to the west, Glen Forrest had at its earliest times a winery on the valley edge down which Hardey Road passes.