- O'Hare
- Oak Brook
- Oak Forest
- Oak Lawn
- Oak Park
- Oakbrook Terrace
- Oakdale
- Oakland (Alameda, California)
- Oakland (Chicago, Illinois)
- Oakland (Orange, Florida)
- Oakland Gardens
- Oakland Park
- Ocala
- Ocean Beach
- Ocean Parkway
- Ocean Ridge
- Ocean View
- Oceana
- Oceanside (Hempstead, New York)
- Oceanside (San Diego, California)
- Ocoee
- Odenton
- Ojai
- Oklahoma City
- Old Bethpage
- Old Lyme
- Old Saybrook
- Old Town (Chicago, Illinois)
- Old Town (Osceola, Florida)
- Old Town (Staten Island, New York)
- Old Westbury
- Old Zionsville
- Olvera Street
- Omaha
- Onancock
- Ontario (San Bernardino, California)
- Opa Locka
- Orange (New Haven, Connecticut)
- Orange (Orange, California)
- Orange City
- Orange County (California)
- Orange County (Florida)
- Orange County (Virginia)
- Orefield
- Orland Park
- Orlando
- Orlo Vista
- Ormond Beach
- Ormrod
- Osceola County
- Oswego
- Overlea
- Oviedo
- Oxford (New Haven, Connecticut)
- Oxford (Talbot, Maryland)
- Oxnard
- Oyster Bay Cove
- Ozone Park
