Cook County, IL (FIPS 17031): Chicago in the Data

Cook County, Illinois (FIPS 17031) is the second most populous county in the United States, with approximately 5.2 million residents. It encompasses the city of Chicago and 130 suburban municipalities, making it one of the most politically and demographically complex counties in the country. The Chicago metro — formally the Chicago-Naperville-Elgin MSA (16980) — extends across 14 counties in Illinois, Indiana, and Wisconsin, but Cook County is by far the largest.

The FIPS code 17031 breaks down as: state 17 (Illinois) + county 031. Cook County's economy is anchored by finance, healthcare, professional services, and manufacturing. O'Hare International Airport (located within Cook County) makes it a major logistics hub. In BLS QCEW data, Cook County's employment in finance and insurance rivals New York's share relative to metro total employment. The Federal Reserve Bank of Chicago publishes extensive research using Cook County and Chicago MSA data.

Cook County is notable in health data — it was among the counties most severely affected during the early COVID-19 pandemic and has been the subject of extensive public health research. CDC WONDER mortality data, CMS Medicare utilization data, and HRSA shortage area designations all show significant intra-county variation between Chicago's Loop and its South and West Side communities — a reminder that county-level averages can obscure important neighborhood-level disparities.

Cook County is also significant in HMDA mortgage data, where lending pattern research has documented longstanding geographic disparities in mortgage origination and denial rates across Chicago's neighborhoods. For researchers working on housing, health, labor markets, or urban economics in the Midwest, Cook County 17031 is a central geography. See the full Cook County profile, browse Illinois counties, or search for any Cook County-adjacent FIPS code.