O Cities in Illinois

Home / Illinois Cities

42 Illinois cities and towns start with O, from O'Fallon to Owaneco. The largest is Orland Park, with an estimated 58,020 people in July 2024, per the US Census Bureau.

O'Fallon Oak Brook Oak Forest Oak Grove Oak Lawn Oak Park Oakbrook Terrace Oakdale Oakford Oakland Oakwood Oakwood Hills Oblong Oconee Odell Odin Ogden Oglesby Ohio Ohlman Okawville Old Mill Creek Old Ripley Old Shawneetown Olmsted Olney Olympia Fields Omaha Onarga Oneida Oquawka Orangeville Oreana Oregon Orient Orion Orland Hills Orland Park Oswego Ottawa Otterville Owaneco