- Oak Park (Population: 29,793)
- Okemos (Population: 22,805)
- Olivet (Population: 1,758)
- Ontonagon (Population: 1,769)
- Orchard Lake Village (Population: 2,215)
- Ortonville (Population: 1,535)
- Ossineke (Population: 1,059)
- Otsego (Population: 3,933)
- Ovid (Population: 1,514)
- Owosso (Population: 15,713)
- Oxford (Population: 3,540)
