Ō
O
- (Sado Shi) Ogi-kowashimizu
- (Sado Shi) Ogi-kinoura
- (Sado Shi) Ogi-ōura
- (Sado Shi) Ogi-kaneta-shinden
- (Kashiwazaki Shi) Onadani
- (Santō-gun) Otomo
- (Nagaoka Shi) Ogunimachi-nihon’yanagi
- (Nagaoka Shi) Ogunimachi-ainohara
- (Nagaoka Shi) Ogunimachi-ōgai
- (Nagaoka Shi) Ogunimachi-yamanota
- (Uonuma Shi) Oritate-matashinden
- (Uonuma Shi) Obirō
- (Sanjō Shi) Ogibori
- (Niigata Shi) Okashinden
- (Shibata Shi) Otoji
- (Higashikambara-gun) Omokura
- (Myoko-shi) Okemi