O
- (Kisarazu Shi) Ogisaku
- (Ichihara Shi) Orizu
- (Ichihara Shi) Okuno
- (Ichihara Shi) Odappe
- (Ichihara Shi) Ogisaku
- (Chōsei-gun) Osakabe
- (Chōsei-gun) Oiwake
- (Chōsei-gun) Ozawa
- (Isumi-gun) Odoro
- (Kimitsu Shi) Ozawa
- (Kimitsu Shi) Okuda
- (Kimitsu Shi) Obitsudai
- (Kimitsu Shi) Owari
- (Kimitsu Shi) Oyashiki
- (Kimitsu Shi) Osaka
Ō
- (Kisarazu Shi) Ōgane
- (Kisarazu Shi) Ōine
- (Ichihara Shi) Ōkura
- (Ichihara Shi) Ōto
- (Ichihara Shi) Ōkubo
- (Ichihara Shi) Ōwada
- (Ichihara Shi) Ōtsubo
- (Ichihara Shi) Ōsaku
- (Ichihara Shi) Ōoke
- (Chōsei-gun) Ōzukura
- (Chōsei-gun) Ōniwa
- (Chōsei-gun) Ōkaba
- (Kimitsu Shi) Ōmori
- (Kimitsu Shi) Ōto
- (Kimitsu Shi) Ōnodai