| Locality | Postal Code |
|---|---|
| Arakuda (古河市) | 306-0044 |
| Asahicho (古河市) | 306-0012 |
| Chayashinden (古河市) | 306-0051 |
| Chozaemonshinden (古河市) | 306-0103 |
| Chuocho (古河市) | 306-0033 |
| Eguchi (古河市) | 306-0105 |
| Gohei (古河市) | 306-0123 |
| Hara (古河市) | 306-0026 |
| Haramachi (古河市) | 306-0025 |
| Hase (古河市) | 306-0035 |
| Hasemachi (古河市) | 306-0034 |
| Heiwamachi (古河市) | 306-0006 |
| Higashi (古河市) | 306-0011 |
| Higashihoncho (古河市) | 306-0013 |
| Higashimanakabashi (古河市) | 306-0107 |
| Higashimorokawa (古河市) | 306-0124 |
| Higashiushigaya (古河市) | 306-0232 |
| Higashiyamata (古河市) | 306-0112 |
| Honcho (古河市) | 306-0023 |
| Inamiya (古河市) | 306-0202 |
| Isagoishinden (古河市) | 306-0224 |
| Isobe (古河市) | 306-0225 |
| Kamihemi (古河市) | 306-0234 |
| Kamiisagoi (古河市) | 306-0223 |
| Kamikatata (古河市) | 306-0128 |
| Kamiono (古河市) | 306-0201 |