Illinois Cities that begin with O

49 cities

City
County
2025 Pop. ↓
Orland ParkCook County56,094
Oak LawnCook County54,125
Oak ParkCook County50,510
OswegoKendall County38,640
O'FallonSt. Clair County31,742
Oak ForestCook County25,424
OttawaLaSalle County18,691
OlneyRichland County8,392
Oak BrookDuPage County7,979
Orland HillsCook County6,388
Olympia FieldsCook County4,410
OglesbyLaSalle County3,599
OregonOgle County3,532
Oakbrook TerraceCook County2,653
Oakwood HillsLake County2,043
OrionHenry County1,708
OkawvilleWashington County1,341
OblongCrawford County1,327
OakwoodVermilion County1,258
OnargaIroquois County1,253
OquawkaHenderson County1,047
OdellLivingston County971
OdinMarion County892
OreanaMacon County837
OrangevilleStephenson County725
OaklandColes County715
Oak RunKnox County704
OgdenChampaign County702
OneidaKnox County661
Olive BranchAlexander County506
Oak GroveMercer County460
OhioBureau County455
OrientFranklin County317
OlmstedPulaski County262
OpdykeJefferson County260
OphiemHenry County238
OakfordMenard County226
OwanecoChristian County203
OakdaleWashington County193
OmahaGallatin County186
Old Mill CreekLake County160
OscoHenry County149
OconeeShelby County136
OhlmanMontgomery County106
Old ShawneetownGallatin County105
OlivetVermilion County93
OttervilleGreene County81
Old RipleyBond County79
OxvilleMorgan County29