| Locality | Post Code |
|---|---|
| Higashiyono (筑西市) | 308-0831 |
| Higuchi (筑西市) | 308-0001 |
| Hosoda (筑西市) | 309-1114 |
| Ichinobe (筑西市) | 308-0827 |
| Ideebisawa (筑西市) | 309-1108 |
| Iida (筑西市) | 308-0835 |
| Iijima (筑西市) | 308-0064 |
| Inanobe (筑西市) | 308-0805 |
| Inari (筑西市) | 308-0106 |
| Inoe (筑西市) | 308-0101 |
| Inuzuka (筑西市) | 308-0117 |
| Ippommatsu (筑西市) | 308-0842 |
| Isami (筑西市) | 308-0853 |
| Isayama (筑西市) | 308-0856 |
| Ishiharada (筑西市) | 308-0055 |
| Ishito (筑西市) | 308-0075 |
| Itabashi (筑西市) | 308-0116 |
| Izumi (筑西市) | 308-0076 |
| Kadoi (筑西市) | 309-1107 |
| Kagesawa (筑西市) | 308-0837 |
| Kajiuchi (筑西市) | 308-0107 |
| Kamihiratsuka (筑西市) | 308-0067 |
| Kamihoshiya (筑西市) | 309-1111 |
| Kamikawanago (筑西市) | 308-0815 |
| Kaminakayama (筑西市) | 308-0017 |
| Kaminishigoya (筑西市) | 300-4502 |