COUNTY · MT
Jefferson County, Montana
Jefferson County is a county in Montana with FIPS code 30043 and an estimated population of 13,048 (Census 2023), 15th largest of 56 in the state.
County facts
- Name
- Jefferson County
- State
- Montana
- Type
- county
- FIPS code
- 30043
- State FIPS
- 30
- Population (2023)
- 13,048
- Change since 2020
- +7.5%
- State rank
- 15 of 56
Population is the Census Bureau’s Vintage 2023 estimate.
Questions
What is the FIPS code for Jefferson County?
Jefferson County, Montana has the five-digit FIPS code 30043: 30 for the state and 043 for the county.
What state is Jefferson County in?
Jefferson County is in Montana.
How do I know if an address is in this county?
Use the address lookup. ZIP codes and city names can cross county lines, so an address is the reliable check.
Sources: U.S. Census Bureau geographic reference files; Census Bureau Population Estimates, Vintage 2023. Last reviewed 2026-10-27.