On March 5, 1895, Sweet Grass County was officially created by the State of Montana. Formed from portions of Park, Meagher, and Yellowstone Counties, its establishment reflected the ongoing process of organizing and defining administrative regions within the young state. The county seat is Big Timber, a community situated along the Yellowstone River.

The creation of Sweet Grass County was driven by the needs of a growing population and the desire for more localized governance to address issues pertinent to the area's ranching, agriculture, and timber industries. This organizational step facilitated local development and provided residents with closer access to governmental services, contributing to the broader development of Montana in the late 19th century.