COUNTY · IL
Jefferson County, Illinois
Jefferson County is a county in Illinois with FIPS code 17081 and an estimated population of 36,320 (Census 2023), 38th largest of 102 in the state.
County facts
- Name
- Jefferson County
- State
- Illinois
- Type
- county
- FIPS code
- 17081
- State FIPS
- 17
- Population (2023)
- 36,320
- Change since 2020
- -1.8%
- State rank
- 38 of 102
Population is the Census Bureau’s Vintage 2023 estimate.
Questions
What is the FIPS code for Jefferson County?
Jefferson County, Illinois has the five-digit FIPS code 17081: 17 for the state and 081 for the county.
What state is Jefferson County in?
Jefferson County is in Illinois.
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.