Fort Smith, MT has a population of 41 and is the 28,375th largest city in the United States. The population density is 30 per sq mi which is 336% higher than the Montana average and 67% lower than the national average. The median age in Fort Smith is 58 which is approximately 45% higher than the Montana average of 40. In Fort Smith, 39% of the population over 15 years of age are married, 79% speak English and 0% speak Spanish. 49% of Fort Smith residents were born in Montana, 51% were born out of state, 0% were born outside of the United States and 0% were foreign born.