Founded in November 24, 1924, Petroleum County is one of 56 counties in the state of Montana. Historically, Petroleum County was formed from Fergus County. The city of Winnett is the county seat. With FIPS code of 69, Petroleum County has a population of 519 and area of 1,654 square miles (4,284 km2).
List of all cities in Petroleum County, MT alphabetically
| City/Town | Postal Code | Area Code |
| Cat Creek, MT | 59087 | 406 |
| Grass Range, MT | 59084 | 406 |
| Teigen, MT | 59084 | 406 |
| Winnett, MT | 59084 | 406 |
| Winnett, MT | 59087 | 406 |