Halfmoon Falls is a 140-foot waterfall on Big Timber Creek in Sweet Grass County, Montana, in the Middle Rockies region. It lies about 20 miles northwest of Big Timber and roughly 85.9 miles west of Billings as the crow flies.
At 140 feet it is on the modest side for Montana, where the typical waterfall with a recorded height stands around 250 feet; it ranks 79th of 123. By form it is a cascade, descending over a series of rock steps rather than in a single drop.
The Middle Rockies are high, glaciated mountain ranges with alpine peaks, subalpine fir and spruce forest, lodgepole pine and grassy intermontane valleys. Snowmelt streams cascade down glacial valleys and canyon walls.
Sweet Grass County holds 6 recorded waterfalls, and several are close by. Thunder Rapids, 480 feet high, is about 1.7 miles away.
Halfmoon Falls is located at 46.0401° N, 110.2485° W. The listing is based on the World Waterfall Database, one of the sources compiled by the U.S. Geological Survey in its inventory of waterfalls and rapids of the conterminous United States. The creek name is confirmed against the federal Geographic Names Information System. The position was verified on aerial imagery. Details on trails, parking and access have not been documented for this waterfall yet.