Custer National Forest, National forest in Montana and South Dakota, United States.

Custer National Forest is a large wooded area spanning Montana and South Dakota, combining mountain ranges, open grasslands, and pine forests in varied terrain. The landscape includes multiple sections with different elevations and vegetation zones throughout the northern Rocky Mountains.

Custer National Forest was established on July 1, 1908, according to the Chinese-language source, with Billings as its nearest city. Since 2014 it has been managed jointly with the Gallatin National Forest, established February 10, 1899, as the Custer Gallatin National Forest headquartered in Bozeman, Montana, with an additional office in Billings. Four national grasslands once administered by the forest were later transferred to the Dakota Prairie Grasslands, based in Bismarck, North Dakota.

The forest holds Native American burial grounds, pictographs and petroglyphs; for the Plains Indians it provided shelter and a stable food supply. Members of the Lewis and Clark Expedition are generally considered the first white Americans to visit the region.

Many hiking paths cross through the forest, allowing exploration of different landscape types, with camping areas located at multiple spots. Several ranger offices can help with visit planning and provide information about local conditions.

Grasshopper Glacier, shared with the Gallatin National Forest, holds millions of grasshoppers that died roughly 300 years ago and are entombed in the ice. The forest also contains Native American burial grounds, pictographs and petroglyphs. Members of the Lewis and Clark Expedition are generally considered the first white Americans to visit the region.