|State||New South Wales|
|Region||Sydney Basin (IBRA), Central Tablelands|
|Municipality||City of Lithgow|
|⁃ location||near Bell|
|Mouth||confluence with the Coxs River|
|at Glenroy, south-west of Hartley|
|Length||10 km (6.2 mi)|
|River system||Hawkesbury-Nepean catchment|
|⁃ left||Dargans Creek|
|⁃ right||Kangaroo Corner Creek|
The River Lett rises on the southern slopes of the Bell Range, below Bell, approximately 10 kilometres (6.2 mi) north of Mount Victoria, and flows generally west south-west, joined by two minor tributaries, before reaching its confluence with the Coxs River, at Glenroy, south-west of the historical settlement of Hartley. The river course is approximately 10 kilometres (6.2 mi).
The Great Western Highway traverses the River Lett near Hartley, at the bottom of the ascent of River Lett Hill. The remains of an old timber bridge that carried traffic on the Great Western Highway over the River Lett can be found near the settlement of Hartley.
- "River Lett". Geographical Names Register (GNR) of NSW. Geographical Names Board of New South Wales. Retrieved 24 December 2013.
- "Concept design and road boundaries: Invitation to comment" (PDF). Mount Victoria to Lithgow: Great Western Highway upgrade. Roads and Maritime Services. July 2012. Retrieved 24 December 2013.
- "Great Western Highway". OzRoads: The Australian Roads Website. Retrieved 24 December 2013.