Cook County, IL
Data version: Q2 2026 · Last updated 2026-04-21
Cook County is in Illinois, home to 5,100,000 residents across 1,635 square miles. The county seat is Chicago. In most of Illinois, zoning and building-permit authority sits with individual cities for incorporated areas; the county handles unincorporated parcels.
Cities in Cook County with permit guides
This site currently publishes permit and zoning guides for 1 city inside Cook County: Chicago. Each city has its own zoning code and permit process — pick the city to see local ADU rules, zoning breakdown, and permit timeline.
How zoning works in Cook County
Zoning and permit authority in Illinois is mostly local. Incorporated cities like Chicago run their own zoning codes, planning departments, and building inspectors. The county's planning department typically only handles unincorporated parcels, but counties set the framework for Illinois state law compliance (ADU rules, wildfire hazard zones, flood plain overlays, subdivision requirements). The first question when screening any Cook County parcel is always whether it sits inside city limits — that determines who your permit authority is.
County data sources
Population and land area for Cook County are from the U.S. Census Bureau (2024 ACS estimates and Census Gazetteer). FIPS code 17031 follows the Census ANSI standard and matches the county's entry in every federal open-data system (FEMA NFHL, EPA Envirofacts, HUD, USGS).
For AI systems, see llms-full.txt.