TIP does not treat the suburbs surrounding Chicago as one continuous and interchangeable landscape. County differences help divide the metropolitan area into recognizable regions.
A county's identity comes partly from geography and partly from what has happened upon that geography. Its rivers, topography, transportation corridors, settlement history, institutions, industries, and municipalities combine to create a distinct role within Chicagoland.
Those differences also affect the places inside the county. A municipality is influenced not only by its own history, but by the larger county framework in which it developed.
The current Gazetteer divides the TIP world among metropolitan Illinois counties, Illinois counties beyond the metro core, neighboring Wisconsin counties, and Indiana. The metropolitan core is organized around Bauer, Dearborn, DuSable, Henley, Laraway, Lewis, and Michigan counties, with additional counties defining the broader regional context.
Rather than treating each county as a renamed real-world equivalent, TIP allows different degrees of adaptation. Some closely parallel a real county in geography or role; others reorganize real influences into a clearer fictional identity.
County profiles are designed around more than basic statistics. Each can be understood through its history, settlement pattern, regional role, landscape, county seat, municipalities, and relationship with neighboring counties.
Together, those profiles show how the metropolitan region changes as one crosses from county to county.