| Locality | Post Code |
|---|---|
| Kamitomioka (長岡市) | 940-2136 |
| Kamitomiokamachi (長岡市) | 940-2137 |
| Kamiya (長岡市) | 949-5407 |
| Kamiyanagimachi (長岡市) | 940-2471 |
| Kanamecho (長岡市) | 940-1153 |
| Kanazawa (長岡市) | 940-0135 |
| Kandamachi (長岡市) | 940-0052 |
| Kanefusa (長岡市) | 940-0045 |
| Kanemachi (長岡市) | 940-0221 |
| Kantomachi (長岡市) | 940-0067 |
| Kanzawa (長岡市) | 940-0153 |
| Karasugashima (長岡市) | 940-0201 |
| Karuizawa (長岡市) | 940-0243 |
| Kashiwacho (長岡市) | 940-0088 |
| Kasuga (長岡市) | 940-0096 |
| Kasujima (長岡市) | 954-0141 |
| Katadamachi (長岡市) | 940-1143 |
| Katsubomachi (長岡市) | 940-0803 |
| Katsuramachi (長岡市) | 940-0802 |
| Kawabemachi (長岡市) | 940-0001 |
| Kawabukuromachi (長岡市) | 940-2463 |
| Kawaguchi Aikawa (長岡市) | 949-7507 |
| Kawaguchi Araya (長岡市) | 949-7508 |
| Kawaguchi Budokubo (長岡市) | 949-7506 |
| Kawaguchi Kizawa (長岡市) | 949-7502 |
| Kawaguchi Nakayama (長岡市) | 949-7503 |