Place
- Northlake, Illinois1
- Oak Brook, Illinois1
- Oak Forest, Illinois1
- Oak Lawn, Illinois1
- Oak Park, Illinois1
- Oakbrook Terrace, Illinois1
- Oakwood Hills, Illinois1
- Old Mill Creek, Illinois1
- Olympia Fields, Illinois1
- Orland Hills, Illinois1
- Orland Park, Illinois1
- Oswego, Illinois1
- Palatine, Illinois1
- Palos Heights, Illinois1
- Palos Hills, Illinois1
- Palos Park, Illinois1
- Park City, Illinois1
- Park Forest, Illinois1
- Park Ridge, Illinois1
- Peotone, Illinois1