Golden Valley County is a county located in the U.S. state of Montana. As of the 2020 census, the population was 823, making it the third-least populous county in Montana. Its county seat is Ryegate. According to the United States Census Bureau, the county has a total area of 1,176 square miles, of which 1,175 square miles is land and 1.0 square mile is wat…Golden Valley County is a county located in the U.S. state of Montana. As of the 2020 census, the population was 823, making it the third-least populous county in Montana. Its county seat is Ryegate. According to the United States Census Bureau, the county has a total area of 1,176 square miles, of which 1,175 square miles is land and 1.0 square mile is water. It is Montana's fifth-smallest county by area.