Founded in January 13, 1913, Big Horn County is one of 56 counties in the state of Montana. Historically, Big Horn County was formed from Rosebud County and Yellowstone County. The city of Hardin is the county seat. With FIPS code of 3, Big Horn County has a population of 12,957 and area of 4,995 square miles (12,937 km2).
List of all cities in Big Horn County, MT alphabetically
| City/Town | Postal Code | Area Code |
| Busby, MT | 59016 | 406 |
| Crow Agency, MT | 59022 | 406 |
| Decker, MT | 59025 | 406 |
| Fort Smith, MT | 59035 | 406 |
| Garryowen, MT | 59031 | 406 |
| Hardin, MT | 59034 | 406 |
| Kirby, MT | 59016 | 406 |
| Lodge Grass, MT | 59050 | 406 |
| Pryor, MT | 59066 | 406 |
| Saint Xavier, MT | 59075 | 406 |
| Wyola, MT | 59089 | 406 |
| Yellowtail, MT | 59035 | 406 |