The county handles building permits for unincorporated areas, while incorporated municipalities like Springfield manage their own building and zoning departments. Development in unincorporated areas is subject to county-specific zoning ordinances and flood hazard regulations managed by the Department of Planning and Zoning.
How this fits with the state
The state authority here is Illinois IDFPR; Illinois Department of Public Health; local building departments. The county file does not replace that — it adds the permit office, local overlays, and the actual filing path.