PO | County | Dates | Comments |
| IDAHO CITY | Boise | 1864-Date | |
| IDAHO FALLS | Bonneville | 1890-Date | was EAGLE ROCK |
| IDAHOME | Cassia | 1914-1942 | |
| IDMON | Clark | 1919-1927 | |
| ILO | Lewis | 1899-1910 | |
| 1911-1920 | renamed CRAIGMONT | ||
| INDEPENDENCE | Madison | 1889-1905 | |
| INIDAN COVE | Owyhee | 1913-1915 | |
| INDIAN CREEK | Elmore | 1873-1874 | |
| INDIAN VALLEY | Adams | 1873-Date | |
| INDIANOLA | Lemhi | 1897-1897 | |
| INKOM | Bannock | 1903-Date | |
| INTERSTATE | Shoshone | 1915-1925 | |
| IOLA | Bonner | 1902-1914 | renamed SAMUELS |
| IONA | Bonneville | 1892-Date | |
| IOWA BAR | Bonneville | 1874-1883 | |
| IRON SPRINGS | Adams | 1903-1908 | |
| IRWIN | Bonneville | 1897-Date | |
| ISLAND | Cassia | 1882-1883 | |
| 1899-1916 | |||
| ISLAND PARK | Fremont | 1911-1916 | |
| 1923-Date | |||
| IVERS | Custer | 1905-1908 | |
| IVY | Latah | 1902-1908 |
Contributed 2021 Oct 05 by Mark Metkin
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