| Code | Name | Region |
|---|---|---|
| JPOCH | Okunouchi | 34 |
| JPOIR | Okushiri | 1 |
| JPOAX | Oma | 2 |
| JPOMC | Omachi | 20 |
| JPOMZ | Omaezaki | 22 |
| JPAOM | Omi | 15 |
| JPOMI | Omi | 38 |
| JPOHH | Omihachiman | 25 |
| JPOMT | Ominato | 2 |
| JPOMS | Omishima | 38 |
| JPOMM | Omitama | 8 |
| JPQOM | Omiya | 8 |
| JPOMY | Omiyaji | 43 |
| JPOMD | Omodaka | 42 |
| JPOMN | Omon | 43 |
| JPOMW | Omonawa | 46 |
| JPOJM | Omosu | 32 |
| JPOMH | Omotehama | 4 |
| JPOMO | Omoto | 3 |
| JPKDP | Okawa | 40 |
| JPOOW | Okawa, Nagasaki | 42 |
| JPOKW | Okawa, Wakayama | 30 |
| JPOKY | Okaya | 20 |
| JPOKJ | Okayama | 33 |
| JPOKZ | Okazaki | 23 |
| JPOK2 | Okegawa | 11 |
| JPOKI | Oki | 32 |
| JPOKN | Okinajima | 7 |
| JPOKA | Okinawa | 47 |
| JPOKE | Okinoerabu | 46 |
| JPOKK | Okinokojima | 46 |
| JPOKC | Okitsu, Chiba | 12 |
| JPOKT | Okitsu, Shizuoka | 22 |
| JPOIU | Okiura, Hiroshima | 34 |
| JPOKX | Okiura, Yamaguchi | 35 |
| JPOKS | Okiuranishi | 35 |
| JPOKG | Okogi | 38 |
| JPOKU | Oku | 47 |
| JPOOJ | Okubo, Kagoshima | 46 |
| JPORA | Ohra | 38 |
| JPOUS | Ohse | 8 |
| JPOSI | Ohshima, Ehime | 38 |
| JPOSS | Ohshima, Fukuoka | 40 |
| JPOOM | Ohshima, Kagawa | 37 |
| JPOSO | Ohshima, Miyazaki | 45 |
| JPOIM | Ohshima, Tokyo | 13 |
| JPOSH | Ohshima, Wakayama | 30 |
| JPHGS | Ohshima/hagi | 35 |
| JPOYM | Ohyama/mitsushima | 42 |
| JPOZJ | Ohzuku | 32 |