FIPS code 17031 is Cook County, Illinois. With a population of 5,225,367 (2022 ACS estimate), it ranks #1 in Illinois and #2 nationally. Cook County is part of the Chicago-Naperville-Elgin, IL-IN. 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
17031
Population
5,225,367
2022 ACS · #2 nationally
Density
5,527.6/mi²
people per sq mile
Land Area
945
sq miles
Urban/Rural
Metro — 1M+ population
RUCC 1
How This FIPS Code Works
The 5-digit FIPS code 17031 is formed by combining the 2-digit state identifier 17 (Illinois) with the 3-digit county identifier 031. Together they uniquely identify Cook County in every US federal dataset. No two counties share the same 5-digit FIPS code.
Census ACS Data for FIPS 17031
From the 2022 ACS 5-year estimates — the same values you'd retrieve by querying the Census API with county FIPS 17031.
Median Household Income
$78,304
ACS B19013_001E
Poverty Rate
13.4%
ACS B17001 (below poverty level)
Median Age
37.5
ACS B01002_001E
Metropolitan Area
Adjacent Counties (8)
Counties that share a border with Cook County. Useful for regional analysis — these are the geographies you'd typically include when studying labor markets, commuting zones, or environmental spillovers around FIPS 17031.
Federal Datasets Using Code 17031
FIPS code 17031 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 17031 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:031",
"in": "state:17",
"key": "YOUR_CENSUS_API_KEY",
}
r = requests.get(url, params=params)
data = r.json() # [[header...], [Cook County, Illinois, income, pop, ...]-- 5-digit combined FIPS (state + county)
SELECT * FROM your_table WHERE county_fips = '17031';
-- Some datasets store state and county separately
SELECT * FROM your_table
WHERE state_fips = '17'
AND county_fips = '031';
-- ⚠ Never cast to integer — leading zeros are lost:
-- county_fips = 17031 is WRONG for this countylibrary(tidycensus)
get_acs(
geography = "county",
variables = c(income = "B19013_001E", pop = "B01003_001E"),
state = "17",
county = "031",
year = 2022
)ZIP Codes in Cook 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 Cook County. Why FIPS ≠ ZIP →
| ZIP Code | % in county |
|---|---|
| 60827 | 100.0% |
| 60005 | 100.0% |
| 60644 | 100.0% |
| 60645 | 100.0% |
| 60646 | 100.0% |
| 60647 | 100.0% |
| 60649 | 100.0% |
| 60651 | 100.0% |
| 60652 | 100.0% |
| 60653 | 100.0% |
| 60654 | 100.0% |
| 60655 | 100.0% |
| 60656 | 100.0% |
| 60657 | 100.0% |
| 60659 | 100.0% |
| 60660 | 100.0% |
| 60661 | 100.0% |
| 60706 | 100.0% |
| 60707 | 100.0% |
| 60712 | 100.0% |
| 60714 | 100.0% |
| 60803 | 100.0% |
| 60804 | 100.0% |
| 60805 | 100.0% |
| 60004 | 100.0% |
| 60008 | 100.0% |
| 60016 | 100.0% |
| 60018 | 100.0% |
| 60022 | 100.0% |
| 60025 | 100.0% |
Showing top 30 of 178 ZIP codes by residential address share.