FIPS code 17121 is Marion County, Illinois. With a population of 37,543 (2022 ACS estimate), it ranks #36 in Illinois and #1253 nationally. Marion County is part of the Centralia, IL. The state FIPS code for Illinois is 17. This code is used in Census Bureau, BLS, EPA, HUD, and USDA federal datasets to identify this county.
County FIPS
17121
Population
37,543
2022 ACS · #1253 nationally
Density
65.6/mi²
people per sq mile
Land Area
572
sq miles
Urban/Rural
Nonmetro — urban 2.5K–19.9K, not adjacent to metro
RUCC 7
How This FIPS Code Works
The 5-digit FIPS code 17121 is formed by combining the 2-digit state identifier 17 (Illinois) with the 3-digit county identifier 121. Together they uniquely identify Marion County in every US federal dataset. No two counties share the same 5-digit FIPS code.
Census ACS Data for FIPS 17121
From the 2022 ACS 5-year estimates — the same values you'd retrieve by querying the Census API with county FIPS 17121.
Median Household Income
$59,099
ACS B19013_001E
Poverty Rate
17.0%
ACS B17001 (below poverty level)
Median Age
41.9
ACS B01002_001E
Metropolitan Area
Adjacent Counties (6)
Counties that share a border with Marion County. Useful for regional analysis — these are the geographies you'd typically include when studying labor markets, commuting zones, or environmental spillovers around FIPS 17121.
Federal Datasets Using Code 17121
FIPS code 17121 appears as the county identifier in the following federal datasets. Analysts joining data across these sources use this code as the common geographic key.
Using FIPS Code 17121 in Code
Common patterns for querying federal datasets by this county's FIPS code. The leading zeros are significant — always treat FIPS codes as strings, not integers.
import requests
url = "https://api.census.gov/data/2022/acs/acs5"
params = {
"get": "NAME,B19013_001E,B01003_001E",
"for": "county:121",
"in": "state:17",
"key": "YOUR_CENSUS_API_KEY",
}
r = requests.get(url, params=params)
data = r.json() # [[header...], [Marion County, Illinois, income, pop, ...]-- 5-digit combined FIPS (state + county)
SELECT * FROM your_table WHERE county_fips = '17121';
-- Some datasets store state and county separately
SELECT * FROM your_table
WHERE state_fips = '17'
AND county_fips = '121';
-- ⚠ Never cast to integer — leading zeros are lost:
-- county_fips = 17121 is WRONG for this countylibrary(tidycensus)
get_acs(
geography = "county",
variables = c(income = "B19013_001E", pop = "B01003_001E"),
state = "17",
county = "121",
year = 2022
)ZIP Codes in Marion County
ZIP codes do not align perfectly with county boundaries — a single ZIP code can span multiple counties, and a county can contain parts of many ZIP codes. The ratios below (from the Census 2020 ZCTA relationship file) show the land area share of each ZCTA that falls within Marion County. Why FIPS ≠ ZIP →
| ZIP Code | % in county |
|---|---|
| 62870 | 100.0% |
| 62807 | 100.0% |
| 62849 | 100.0% |
| 62881 | 100.0% |
| 62853 | 100.0% |
| 62854 | 98.2% |
| 62892 | 90.4% |
| 62882 | 82.8% |
| 62875 | 57.4% |
| 62893 | 45.1% |
| 62801 | 37.0% |
| 62889 | 32.3% |
| 62838 | 7.9% |
| 62830 | 4.1% |
| 62851 | 2.4% |