PO | County | Dates | Comments |
| ALDER | Custer | 1884-1885 | |
| ALEXANDER | Caribou | 1903-1953 | |
| ALMEDA | Latah | 1892-1893 | |
| ALMO | Cassia | 1882-Date | |
| ALPHA | Valley | 1888-1954 | |
| ALPINE | Adams | 1891-1907 | |
| ALPINE | Bonneville | 1910-1918 | in Idaho |
| 1918-1934 | in Wyoming | ||
| 1936-1940 | in Idaho | ||
| 1940-1942 | in Wyoming | ||
| 1942-1956 | in Idaho | ||
| 1956-1959 | in Wyoming | ||
| ALRIDGE | Bingham | 1915-1917 | |
| 1921-1950 | |||
| ALTA | Twin Falls | 1911-1912 | |
| ALTON | Bear Lake | 1902-1908 | |
| AMERICAN FALLS | Power | 1882-Date | |
| AMMON | Power | 1898-1906 | |
| AMSTERDAM | Twin Falls | 1912-1918 | |
| 1919-1954 | |||
| AMWACO | Kootenai | 1910-1921 | |
| ANDERSON | Latah | 1893-1907 | renamed DEARY |
| ANDERSON DAM | Elmore | 1942-1950 | |
| ANNIS | Jefferson | 1896-1906 | |
| ANTELOPE | Bonneville | 1914-1925 | |
| ANTELOPE | Butte | 1882-1887 | |
| 1888-1902 | renamed DARLINGTON | ||
| APPLETON | Gooding | 1911-1914 | |
| ARANGEE | Fremont | 1891-1898 | renamed REA |
| ARBON | Power | 1898-Date | |
| ARCHER | Madison | 1902-1920 | |
| ARCO | Butte | 1880-Date | |
| ARGORA | Clark | 1916-1939 | |
| ARIMO | Bannock | 1912-Date | was ONEIDA |
| ARLING | Valley | 1915-1920 | |
| 1920-1941 | |||
| ARROWROCK | Boise | 1911-1917 | |
| ARTESIAN CITY | Twin Falls | 1909-1913 | |
| ASHTON | Fremont | 1906-Date | |
| ATHOL | Kootenai | 1895-Date | |
| ATLANTA | Elmore | 1870-1880 | was ATLANTA CITY |
| 1880-1995 | |||
| ATLANTA CITY | Elmore | 1867-1870 | renamed ATLANTA |
| ATOMIC CITY | Bingham | 1950-Date | |
| AUSTIN | Twin Falls | 1898-1910 | |
| AVERY | Shoshone | 1910-Date | was PINCHOT |
| AVON | Latah | 1891-1953 | |
Contributed 2021 Oct 05 by Mark Metkin
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