Founded in February 2, 1865, Jefferson County is one of 56 counties in the state of Montana. Historically, Jefferson County was one of the 9 original counties. The city of Boulder is the county seat. With FIPS code of 43, Jefferson County has a population of 12,470 and area of 1,657 square miles (4,292 km2).
List of all cities in Jefferson County, MT alphabetically
|City/Town||Postal Code||Area Code|
|Jefferson City, MT||59638||406|
|Montana City, MT||59634||406|