COUNTY · IL
Cass County, Illinois
Cass County is a county in Illinois with FIPS code 17017 and an estimated population of 12,596 (Census 2023), 81st largest of 102 in the state.
County facts
- Name
- Cass County
- State
- Illinois
- Type
- county
- FIPS code
- 17017
- State FIPS
- 17
- Population (2023)
- 12,596
- Change since 2020
- -3.0%
- State rank
- 81 of 102
Population is the Census Bureau’s Vintage 2023 estimate.
Questions
What is the FIPS code for Cass County?
Cass County, Illinois has the five-digit FIPS code 17017: 17 for the state and 017 for the county.
What state is Cass County in?
Cass 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.