| State Name | County Name | City |
|---|---|---|
| Missouri | St. Louis | Oakville |
| Georgia | Hall | Oakwood |
| Ohio | Montgomery | Oakwood - Montgomery |
| Ohio | Cuyahoga | Oakwood - Cuyahoga |
| California | Riverside | Oasis |
| Oregon | Clackamas | Oatfield |
| Ohio | Lorain | Oberlin |
| Ohio | Franklin | Obetz |
| Florida | Marion | Ocala |
| New Jersey | Monmouth | Ocean |
| New Jersey | Ocean | Ocean Acres |
| Massachusetts | Plymouth | Ocean Bluff-Brant Rock |
| Florida | Okaloosa | Ocean City |
| Maryland | Worcester | Ocean City |
| New Jersey | Cape May | Ocean City |
| Massachusetts | Bristol | Ocean Grove |
| New Jersey | Monmouth | Ocean Grove |
| Maryland | Worcester | Ocean Pines |
| Hawaii | Honolulu | Ocean Pointe |
| Washington | Grays Harbor | Ocean Shores |
| Mississippi | Jackson | Ocean Springs |
| Delaware | Sussex | Ocean View |
| California | San Luis Obispo | Oceano |
| New Jersey | Monmouth | Oceanport |
| California | San Diego | Oceanside |
| New York | Nassau | Oceanside |
| Georgia | Irwin | Ocilla |
| Florida | Orange | Ocoee |
| Wisconsin | Oconto | Oconto |
| Wisconsin | Oconto | Oconto Falls |
| Maryland | Anne Arundel | Odenton |
| Alabama | St. Clair | Odenville |
| Florida | Pasco | Odessa |
| Missouri | Lafayette | Odessa |
| Texas | Ector | Odessa |
| Illinois | St. Clair | O'Fallon |
| Missouri | St. Charles | O'Fallon |
| Nebraska | Sarpy | Offutt AFB |
| Nebraska | Keith | Ogallala |
| North Carolina | New Hanover | Ogden |
| New York | Monroe | Ogden |
| Utah | Weber | Ogden |
| New York | St. Lawrence | Ogdensburg |
| Illinois | LaSalle | Oglesby |
| Pennsylvania | Allegheny | O'Hara |
| Pennsylvania | Allegheny | Ohio |
| Pennsylvania | Beaver | Ohioville |
| Pennsylvania | Venango | Oil City |
| California | Kern | Oildale |
| California | Ventura | Ojai |
| Florida | Miami-Dade | Ojus |
| Wisconsin | Waukesha | Okauchee Lake |
| Florida | Okeechobee | Okeechobee |
| Oklahoma | Okfuskee | Okemah |
| Michigan | Ingham | Okemos |
| Oklahoma | Oklahoma | Oklahoma City |
| Oklahoma | Okmulgee | Okmulgee |
| New York | Nassau | Old Bethpage |
| New Jersey | Middlesex | Old Bridge |
| California | Fresno | Old Fig Garden |
| Pennsylvania | Lackawanna | Old Forge |
| Connecticut | Fairfield | Old Greenwich |
| Missouri | St. Louis | Old Jamestown |
| Louisiana | East Baton Rouge | Old Jefferson |
| Pennsylvania | Lycoming | Old Lycoming |
| Connecticut | New London | Old Lyme |
| Connecticut | New London | Old Mystic |
| Maine | York | Old Orchard Beach |
| Texas | Chambers | Old River-Winfree |
| Connecticut | Middlesex | Old Saybrook |
| New Jersey | Bergen | Old Tappan |
| Maine | Penobscot | Old Town |
| New York | Nassau | Old Westbury |
| Florida | Pinellas | Oldsmar |
| New York | Cattaraugus | Olean |
| Pennsylvania | Berks | Oley |
| Texas | Hidalgo | Olivarez |
| New York | Ulster | Olive |
| Mississippi | DeSoto | Olive Branch |
| California | Yuba | Olivehurst |
| Tennessee | Roane | Oliver Springs |
| Missouri | St. Louis | Olivette |
| Ohio | Cuyahoga | Olmsted Falls |
| Illinois | Richland | Olney |
| Maryland | Montgomery | Olney |
| Texas | Young | Olney |
| Washington | Thurston | Olympia |
| Illinois | Cook | Olympia Fields |
| Florida | Miami-Dade | Olympia Heights |
| Pennsylvania | Lackawanna | Olyphant |
| Nebraska | Douglas | Omaha |
| Washington | Okanogan | Omak |
| Wisconsin | Winnebago | Omro |
| Texas | Polk | Onalaska |
| Wisconsin | La Crosse | Onalaska |
| New York | Madison | Oneida |
| Tennessee | Scott | Oneida |
| Wisconsin | Waukesha | Oconomowoc |
| Iowa | Fayette | Oelwein |
| Kansas | Johnson | Olathe |
