St. Clair

St. Clair is a county inside Illinois (FIPS code 17163) that contains 28 USPS ZIP codes covering a combined population of 269,095 according to Census ACS 5-Year Estimates. Counties are the natural bridge between state-level summaries and ZIP-level detail — crime statistics, HUD Fair Market Rents, and childcare pricing are all published at the county level, while household income and housing values are published at the ZIP level. This page reconciles the two views so you can see which ZIPs drive the county totals.

The 28 ZIPs listed below are ordered by population and each links to the full ZIP detail page with Census demographics, housing, income, home-price history, and cross-agency inputs. The most populated ZIP in St. Clair is 62269 covering O Fallon with 31,348 residents at 448 people per square mile. Population density across ZIPs in this county varies — use the density column to spot urban cores versus rural delivery areas. A single county can contain both a dense downtown ZIP and a large rural ZIP covering several hundred square miles.

Because St. Clair uses FIPS code 17163, it joins cleanly to county-level federal datasets: HUD Fair Market Rent tables, FBI Uniform Crime Report data, and the Department of Labor National Database of Childcare Prices all key off the same code. That is how neighborhood scorecards combine ZIP-level Census demographics with county-level safety and affordability metrics. All data on this page comes from U.S. Census Bureau ACS 2023 5-Year Estimates and USPS ZIP Code Tabulation Area files — no estimates, no proprietary sources, no editorial scoring.