Ravalli County is a county in the southwestern part of the U.S. state of Montana. As of the 2020 census, the population was 44,174. Its county seat is Hamilton. Ravalli County is part of a north–south mountain valley bordered by the Sapphire Mountains on the East and the Bitterroot Mountains on the West. It is often referred to as the Bitterroot Valley, which is named for the Bitterroot Flower.