PO | County | Dates | Comments |
| UCON | Bonneville | 1910-Date | |
| ULYSSES | Lemhi | 1902-1929 | |
| UNION | Canyon | 1866-1868 | |
| UNION | Madison | 1899-1907 | |
| UNION | Shoshone | 1910-1918 | was WALKER |
| UPPER SQUAW CREEK | Gem | 1875-1877 | |
| USTICK | Ada | 1908-1958 |
Contributed 2021 Oct 05 by Mark Metkin
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