· Oak Park, Michigan
· Oak Ridge, Tennessee
· Oakdale, Minnesota
· Oakes, North Dakota
· Oakland, California
· Oakland City, Indiana
· Oberhausen, Germany
· Ocilla, Georgia
· Ocumare del Tuy, Venezuela
· Odense, Denmark
· Odessa, Texas
· Odivelas, Portugal
· O'Fallon, Illinois
· Ogbomosho, Nigeria
· Ogden, Utah
· Oil City, Pennsylvania
· Oklahoma City, Oklahoma
· Olathe, Kansas
· Olavarria, Argentina
· Olbia, Italy
· Olean, New York
· Olsztyn, Poland
· Olten, Switzerland
· Olympia, Washington
· Omaha, Nebraska
· Omsk, Russia
· Onida, South Dakota
· Opelika, Alabama
· Opelousas, Louisiana
· Oran, Algeria
· Orange, Australia
· Orangeburg, South Carolina
· Ordu, Turkey
· Oregon, Ohio
· Oregon City, Oregon
· Orel, Russia
· Orestiada, Greece
· Orlando, Florida
· Orleans, France
· Orofino, Idaho
· Oruro, Bolivia
· Osaka, Japan
· Osasco, Brazil
· Oshkosh, Wisconsin
· Oslo, Norway
· Osnabruck, Germany
· Osorno, Chile
· Ostrava, Czech Republic
· Ostend, Belgium
· Ottawa, Canada
· Ottumwa, Iowa
· Ouagadougou, Burkina Faso
· Ouargla, Algeria
· Oujda, Morocco
· Oulu, Finland
· Ovalle, Chile
· Overland Park, Kansas
· Oviedo, Spain
· Owensboro, Kentucky
· Oxford, North Carolina
· Ozark, Arkansas
OregonOxford
Ocala
I am not aware of any cities in Massachusetts that start with the letter O. However, Oxford, Orange, Orleans, Oak Bluff, and Otis are towns in Massachusetts.
Reno, Nevada or Rio Claro, Colombia
i don't know many but there is one called ohio- in america.
Orange is a city in New South Wales, Australia.
Cities in Illinois that start with the letter T:TaylorvilleTolucaToulonTroyTuscola
Cities in Pennsylvania that start with the letter H:HarrisburgHazletonHermitage
oakland oak harbor oman oakland oak harbor oman
Orange City, FL Oakland, CA Oakland, MI
orlando, florida orange county, california oklahoma city, oklahoma
Counties in Iowa that start with the letter O:O'Brien CountyOsceola CountySome of the cities in Iowa that start with the letter O:OaklandOdeboltOelweinOgdenOnawaOrange CityOsageOsceolaOskaloosaOttumwaRivers in Iowa that start with the letter O:Ocheyedan River