Treasure County is a county in the U.S. state of Montana. As of the 2020 census, the population was 762, making it the second-least populous county in Montana. Its county seat is Hysham. The county was founded in 1919.

Big Horn County is a county located in the U.S. state of Montana. As of the 2020 census, the population was 13,124. The county seat is Hardin. The county, like the river and the mountain range, is named after the bighorn sheep in the Rocky Mountains. The county was founded in 1913. It is located on the south line of the state.