PO | County | Dates | Comments |
| SAGLE | Bonner | 1900-Date | |
| SAINT ANTHONY | Fremont | 1888-Date | |
| SAINT CHARLES | Bear Lake | 1867-Date | |
| SAINT JOE | Benewah | 1888-1895 | |
| 1896-1903 | |||
| 1905-1945 | was FERRELL | ||
| SPO 1931-1945 | |||
| SAINT JOHN | Oneida | 1879-1880 | |
| SAINT JOHNS | Oneida | 1888-1892 | |
| SAINT MARIES | Benewah | 1889-Date | |
| SALEM | Madison | 1893-1916 | |
| SALMON | Lemhi | 1895-Date | was SALMON CITY |
| SALMON CITY | Lemhi | 1869-1895 | renamed SALMON |
| SALMON FALLS | Gooding | 1889-1895 | |
| SALMON FALLS | Twin Falls | 1879-1884 | |
| 1884-1888 | |||
| SALUBRIA | Washington | 1870-1908 | |
| 1911-1916 | |||
| SAM | Teton | 1925-1937 | |
| SAMARIA | Oneida | 1881-1963 | |
| SAMUELS | Bonner | 1914-1985 | was IOLA |
| SAND HOLE | Jefferson | 1878-1878 | |
| SANDERS | Benewah | 1901-1973 | |
| SANDPOINT | Bonner | 1893-Date | was PEND D'OREILLE |
| SANTA | Benewah | 1887-Date | |
| SARILDA | Fremont | 1894-1906 | |
| SATER | Washington | 1883-1887 | |
| SAWTOOTH | Blaine | 1880-1887 | |
| 1887-1896 | |||
| SAWYER | Bonner | 1904-1930 | |
| SAYERS | Jefferson | 1900-1905 | |
| SCHERRER | Minidoka | 1905-1907 | renamed ACEQUIA |
| SEAFOAM | Custer | 1927-1928 | |
| SEBESTA | Benewah | 1915-1925 | |
| SENEAGUOTEEN | Bonner | 1891-1891 | renamed SENEAQUOTEEN |
| SENEAQUOTEEN | Bonner | 1891-1902 | was SENEAGUOTEEN |
| operated as SENEAGUOTEEN | |||
| renamed VALLEY | |||
| SETTERS | Kootenai | 1916-1924 | |
| SEVERANCE | Bonner | 1904-1911 | renamed CAREYWOOD |
| SHAFER | Boise | 1882-1888 | |
| SHARON | Bear Lake | 1901-1915 | |
| SHAWS | Boise | 1880-1880 | |
| SHEARER'S FERRY | Idaho | 1874-1876 | |
| 1879-1885 | |||
| 1886-1888 | |||
| SHEIK | Lemhi | 1923-1927 | |
| SHELLEY | Bingham | 1893-Date | |
| SHEPHARDSVILLE | Ada | 1867-1869 | |
| SHERIDAN | Fremont | 1895-1897 | |
| SHERIDAN | Kootenai | 1884-1884 | was COEUR D'ALENE |
| SHERMAN | Kootenai | 1887-1899 | |
| SHOSHONE | Jerome | 1870-1871 | |
| SHOSHONE | Lincoln | 1883-Date | was NAPLES |
| SHOSHONE FALLS | Jerome | 1884-1886 | |
| SHOUP | Lemhi | 1883-1964 | now CPO |
| SILVER CITY | Owyhee | 1867-1943 | was RUBY CITY |
| SILVER KING | Shoshone | 1900-1906 | |
| SILVERTIP | Benewah | 1914-1918 | |
| SILVERTON | Shoshone | 1941-Date | |
| SINCLAIR | Boundary | 1914-1933 | |
| SINGISER | Lemhi | 1897-1898 | |
| 1898-1901 | |||
| SINKER | Owyhee | 1888-1902 | |
| 1904-1909 | |||
| SKEEN | Cassia | 1881-1881 | |
| SLATE CREEK | Idaho | 1863-1870 | |
| 1871-1879 | |||
| SLICKPOO | Nez Perce | 1898-1926 | |
| SMALL | Clark | 1890-1959 | was MEDICINE LODGE |
| SMELTERVILLE | Shoshone | 1929-Date | |
| SMITHS FERRY | Valley | 1913-1964 | was FERN |
| SMOKY | Blaine | 1882-1882 | |
| 1884-1884 | |||
| 1885-1888 | |||
| SNOW | Nez Perce | 1905-1922 | |
| SNYDER | Boundary | 1908-1913 | |
| SODA SPRINGS | Caribou | 1864-1866 | |
| 1871-Date | |||
| SOLDIER | Camas | 1882-1922 | |
| SORRENTO | Benewah | 1914-1926 | |
| SOUTH BOISE | Ada | 1907-1915 | |
| SOUTH MOUNTAIN | Owyhee | 1872-1874 | |
| 1875-1877 | |||
| SOUTHMOUNTAIN | Owyhee | 1900-1902 | |
| SOUTHWICK | Nez Perce | 1888-1973 | |
| SPALDING | Nez Perce | 1897-1997 | was SPAULDING |
| SPAULDING | Nez Perce | 1897-1897 | renamed SPALDING |
| SPENCER | Clark | 1897-1985 | |
| SPINK | Valley | 1906-1914 | |
| SPIRIT LAKE | Kootenai | 1903-Date | |
| SPRING | Washington | 1885-1898 | |
| SPRING CAMP | Idaho | 1915-1922 | |
| SPRING MOUNTAIN | Lemhi | 1881-1888 | |
| SPRINGFIELD | Bingham | 1905-1963 | now CPO |
| SPRINGSTON | Kootenai | 1901-1955 | |
| SPRINGVAIL | Bingham | 1887-1887 | |
| SQUAW CREEK | Gem | 1870-1889 | renamed MARSH |
| SQUIRREL | Fremont | 1900-1979 | |
| STANDROD | Cassia | 1890-1909 | in Idaho |
| 1909-1914 | in Utah | ||
| 1915-1919 | in Idaho | ||
| STANFIELD | Blaine | 1908-1908 | |
| STANLEY | Custer | 1892-1895 | |
| 1899-1902 | |||
| 1902-Date | |||
| STANTON | Blaine | 1884-1886 | |
| 1889-1914 | |||
| STAR | Ada | 1880-Date | |
| STARKEY | Adams | 1906-1943 | was EVERGREEN |
| STARNER | Latah | 1890-1894 | renamed PRINCETON |
| STARRHS FERRY | Cassia | 1909-1912 | |
| STATION | Idaho | 1900-1901 | |
| STAUSS | Clearwater | 1896-1896 | |
| STEAM SPRINGS | Franklin | 1872-1874 | |
| STEELE | Lewis | 1896-1923 | |
| STERLING | Bingham | 1911-1978 | was OTIS |
| STERRETT | Bannock | 1900-1909 | |
| STEUNENBERG | Idaho | 1909-1910 | operated as STEUNENBURG |
| STEWART | Shoshone | 1911-1918 | |
| STIBNITE | Valley | 1929-1957 | |
| STINSON | Kootenai | 1901-1910 | |
| STITES | Idaho | 1900-Date | |
| STOCK | Bannock | 1916-1917 | |
| STONE | Oneida | 1895-1985 | |
| STREVELL | Cassia | 1913-1924 | |
| STRICKER | Twin Falls | 1904-1910 | |
| STUART | Idaho | 1896-1902 | renamed KOOSKIA |
| SUBLETT | Cassia | 1880-1880 | |
| 1882-1942 | |||
| SUGAR | Madison | 1904-1950 | renamed SUGAR CITY |
| SUGAR CITY | Madison | 1950-Date | was SUGAR |
| SUMMIT | Nez Perce | 1900-1934 | |
| SUN VALLEY | Blaine | 1937-1943 | |
| 1946-Date | |||
| SUNBEAM | Custer | 1907-1912 | |
| 1939-1962 | SPO | ||
| SUNFIELD | Lemhi | 1905-1911 | was HOVER |
| renamed TENDOY | |||
| SUNNYDELL | Madison | 1900-1922 | |
| SUNNYSIDE | Elmore | 1907-1930 | |
| SUNSET | Shoshone | 1913-1920 | |
| 1928-1929 | |||
| SWAN LAKE | Bannock | 1880-1883 | |
| 1886-1894 | renamed SWANLAKE | ||
| SWAN VALLEY | Bonneville | 1917-Date | |
| SWANLAKE | Bannock | 1894-1895 | was SWAN LAKE |
| 1896-Date | |||
| SWEET | Gem | 1885-1967 | now CPO |
| SWEET SAGE | Butte | 1910-1918 | |
| SWEETWATER | Nez Perce | 1903-1955 | |
| SYRINGA | Idaho | 1896-1908 | renamed LOWELL |
Contributed 2021 Oct 05 by Mark Metkin
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