| Locality | Postal Code |
|---|---|
| Postal/ZIP Codes in Tatsumidai Higashi (市原市) | 290-0003 |
| Postal/ZIP Codes in Tatsumidai Nishi (市原市) | 290-0004 |
| Postal/ZIP Codes in Terayatsu (市原市) | 290-0236 |
| Postal/ZIP Codes in Tokuji (市原市) | 290-0544 |
| Postal/ZIP Codes in Tonobeta (市原市) | 290-0551 |
| Postal/ZIP Codes in Toyonari (市原市) | 299-0122 |
| Postal/ZIP Codes in Tozura (市原市) | 290-0536 |
| Postal/ZIP Codes in Tsuchiu (市原市) | 290-0215 |
| Postal/ZIP Codes in Tsuiheiji (市原市) | 290-0032 |
| Postal/ZIP Codes in Tsukide (市原市) | 290-0527 |
| Postal/ZIP Codes in Tsukizaki (市原市) | 290-0547 |
| Postal/ZIP Codes in Tsurumai (市原市) | 290-0512 |
| Postal/ZIP Codes in Uehara (市原市) | 290-0222 |
| Postal/ZIP Codes in Umatate (市原市) | 290-0221 |
| Postal/ZIP Codes in Uruido (市原市) | 290-0171 |
| Postal/ZIP Codes in Uruidominami (市原市) | 290-0170 |
| Postal/ZIP Codes in Ushiku (市原市) | 290-0225 |
| Postal/ZIP Codes in Wakamiya (市原市) | 290-0006 |