COUNTY · IL
Montgomery County, Illinois
Montgomery County is a county in Illinois with FIPS code 17135 and an estimated population of 27,663 (Census 2023), 48th largest of 102 in the state.
County facts
- Name
- Montgomery County
- State
- Illinois
- Type
- county
- FIPS code
- 17135
- State FIPS
- 17
- Population (2023)
- 27,663
- Change since 2020
- -1.9%
- State rank
- 48 of 102
Population is the Census Bureau’s Vintage 2023 estimate.
Questions
What is the FIPS code for Montgomery County?
Montgomery County, Illinois has the five-digit FIPS code 17135: 17 for the state and 135 for the county.
What state is Montgomery County in?
Montgomery 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.