The Sweet Grass Hills (Blackfoot: kátoyissiksi, Cheyenne: vé'ho'ôhtsévóse, Kalispel-Pend d'Oreille: ččaɫalqn, "three peaks"[1]) are a small group of low mountains rising more than 3,000 feet (910 m) above the surrounding plains southwest of Whitlash, Montana, in Liberty and Toole County, Montana.

Visibility may vary depending on local air temperatures or heat domes that may increase or decrease the apparent height of the features.

These island ranges, completely surrounded by the 'sea' of plains and not geographically (or often geologically) part of the Rocky Mountains to the west, are "biological hotspots", containing more species than the prairie below.

The hills were formed in the early Paleogene period, and geologically are known as stocks - intrusive igneous rock forced up from below and solidified.

The Sweet Grass Hills are a sacred site of the Blackfoot aboriginal people who live on both sides of the 49th parallel north which forms the Canada–United States border.