Cumberland State Forest, State forest in West Pennant Hills, Sydney, Australia.

Cumberland State Forest is a 40-hectare wet sclerophyll forest on the southern edge of the Hornsby Plateau in West Pennant Hills. Its northern part, on Wianamatta Shale soils, is dominated by Sydney blue gum and grey ironbark, while turpentine becomes more common on sandstone-influenced ground to the south. A 3.4 km sealed road runs through the forest.

The woodland was acquired by the New South Wales Forestry Commission in 1938 and officially established as a state forest in 1939. This creation protected a natural space within an urban region.

The forest's name comes from the Cumberland Plain, and its arboretum holds rainforest trees rare in the wild, such as Austrobuxus swainii, named after E. H. F. Swain, the commissioner who ordered the 1937 search for the site. The Forestry Corporation of NSW runs volunteer and school holiday activity programs here, and TreeTops Adventure Park has operated a high ropes course since December 2016.

Visitors will find four picnic areas with barbecue facilities and a cafe that operates during daytime hours. The walking tracks are relatively short, making the site accessible for different fitness levels.

It is Australia's only metropolitan state forest and forms a natural wildlife corridor connecting Lake Parramatta Reserve with Berowra Valley National Park. This link allows animals to move between the two protected areas.