Illinois frost dates: S
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Sadorus | Apr 19 | Oct 17 | 181 d | 6a |
| Sailor Springs | Apr 9 | Oct 24 | 198 d | 6b |
| Saint Anne | Apr 19 | Oct 24 | 188 d | 5b |
| Saint Augustine | Apr 22 | Oct 19 | 180 d | 5b |
| Saint Charles | Apr 25 | Oct 19 | 177 d | 5b |
| Saint David | Apr 17 | Oct 19 | 185 d | 6a |
| Saint Elmo | Apr 3 | Oct 24 | 204 d | 6b |
| Saint Francisville | Apr 12 | Oct 25 | 196 d | 6b |
| Saint Jacob | Apr 12 | Oct 20 | 191 d | 7a |
| Saint Joseph | Apr 20 | Oct 21 | 184 d | 6a |
| Saint Libory | Apr 12 | Oct 20 | 191 d | 6b |
| Saint Peter | Apr 3 | Oct 24 | 204 d | 6b |
| Sainte Marie | Apr 13 | Oct 22 | 192 d | 6b |
| Salem | Apr 9 | Oct 26 | 200 d | 6b |
| San Jose | Apr 17 | Oct 18 | 184 d | 6a |
| Sandoval | Apr 9 | Oct 26 | 200 d | 6b |
| Sandwich | Apr 28 | Oct 13 | 168 d | 5b |
| Saunemin | Apr 16 | Oct 24 | 191 d | 5b |
| Savanna | May 2 | Oct 7 | 158 d | 5a |
| Savoy | Apr 15 | Oct 24 | 192 d | 6a |
| Sawyerville | Apr 14 | Oct 21 | 190 d | 6b |
| Saybrook | Apr 21 | Oct 17 | 179 d | 6a |
| Scales Mound | Apr 26 | Oct 15 | 172 d | 5a |
| Schaumburg | Apr 30 | Oct 13 | 166 d | 5b |
| Scheller | Apr 4 | Oct 27 | 206 d | 6b |
| Schiller Park | Apr 16 | Oct 28 | 195 d | 6a |
| Sciota | Apr 21 | Oct 19 | 181 d | 5b |
| Scott Air Force Base | Apr 12 | Oct 20 | 191 d | 6b |
| Scottville | Apr 13 | Oct 22 | 192 d | 6b |
| Seaton | Apr 22 | Oct 19 | 180 d | 5b |
| Seatonville | Apr 24 | Oct 17 | 176 d | 5b |
| Secor | Apr 21 | Oct 17 | 179 d | 5b |
| Seneca | Apr 27 | Oct 17 | 173 d | 5b |
| Serena | Apr 27 | Oct 17 | 173 d | 5b |
| Sesser | Apr 4 | Oct 27 | 206 d | 6b |
| Seward | Apr 26 | Oct 13 | 170 d | 5b |
| Seymour | Apr 23 | Oct 13 | 173 d | 6a |
| Shabbona | Apr 28 | Oct 10 | 165 d | 5b |
| Shannon | Apr 29 | Oct 7 | 161 d | 5a |
| Shawneetown | Apr 5 | Oct 31 | 209 d | 7a |
| Sheffield | Apr 24 | Oct 14 | 173 d | 5b |
| Shelbyville | Apr 10 | Oct 24 | 197 d | 6a |
| Sheldon | Apr 23 | Oct 14 | 174 d | 5b |
| Sheridan | Apr 27 | Oct 17 | 173 d | 5b |
| Sherman | Apr 14 | Oct 20 | 189 d | 6a |
| Sherrard | Apr 24 | Oct 18 | 177 d | 5b |
| Shipman | Apr 14 | Oct 21 | 190 d | 6b |
| Shirland | May 1 | Oct 12 | 164 d | 5b |
| Shirley | Apr 21 | Oct 20 | 182 d | 6a |
| Shobonier | Apr 10 | Oct 24 | 197 d | 6b |
| Shorewood | Apr 19 | Oct 25 | 189 d | 5b |
| Shumway | Apr 13 | Oct 24 | 194 d | 6b |
| Sibley | Apr 21 | Oct 17 | 179 d | 6a |
| Sidell | Apr 19 | Oct 19 | 183 d | 6a |
| Sidney | Apr 20 | Oct 21 | 184 d | 6a |
| Sigel | Apr 16 | Oct 20 | 187 d | 6b |
| Silvis | Apr 16 | Oct 25 | 192 d | 5b |
| Simpson | Apr 14 | Oct 21 | 190 d | 7a |
| Sims | Apr 7 | Oct 26 | 202 d | 6b |
| Skokie | Apr 26 | Oct 21 | 178 d | 6a |
| Smithboro | Apr 10 | Oct 24 | 197 d | 6b |
| Smithfield | Apr 17 | Oct 22 | 188 d | 6a |
| Smithshire | Apr 22 | Oct 14 | 175 d | 5b |
| Smithton | Apr 12 | Oct 20 | 191 d | 7a |
| Somonauk | Apr 28 | Oct 13 | 168 d | 5b |
| Sorento | Apr 13 | Oct 24 | 194 d | 6b |
| South Beloit | May 1 | Oct 12 | 164 d | 5b |
| South Elgin | Apr 26 | Oct 18 | 175 d | 5b |
| South Holland | Apr 23 | Oct 20 | 180 d | 6a |
| South Pekin | Apr 16 | Oct 23 | 190 d | 6a |
| South Roxana | Apr 4 | Nov 5 | 215 d | 7a |
| South Wilmington | Apr 27 | Oct 15 | 171 d | 5b |
| Sparland | Apr 20 | Oct 17 | 180 d | 5b |
| Sparta | Apr 12 | Oct 22 | 193 d | 7a |
| Speer | Apr 22 | Oct 14 | 175 d | 5b |
| Spring Grove | Apr 23 | Oct 21 | 181 d | 5b |
| Spring Valley | Apr 24 | Oct 18 | 177 d | 5b |
| Springerton | Apr 11 | Oct 21 | 193 d | 7a |
| Springfield | Apr 15 | Oct 22 | 190 d | 6a |
| Standard | Apr 24 | Oct 18 | 177 d | 5b |
| Stanford | Apr 21 | Oct 20 | 182 d | 6a |
| Staunton | Apr 13 | Oct 24 | 194 d | 6b |
| Steeleville | Apr 12 | Oct 22 | 193 d | 7a |
| Steger | Apr 23 | Oct 20 | 180 d | 6a |
| Sterling | Apr 21 | Oct 19 | 181 d | 5b |
| Steward | Apr 26 | Oct 13 | 170 d | 5b |
| Stewardson | Apr 16 | Oct 20 | 187 d | 6b |
| Stillman Valley | Apr 24 | Oct 17 | 176 d | 5b |
| Stockland | Apr 25 | Oct 13 | 171 d | 5b |
| Stockton | Apr 27 | Oct 9 | 165 d | 5a |
| Stone Park | Apr 16 | Oct 28 | 195 d | 6a |
| Stonefort | Apr 7 | Oct 26 | 202 d | 7a |
| Stonington | Apr 14 | Oct 24 | 193 d | 6a |
| Stoy | Apr 13 | Oct 22 | 192 d | 6b |
| Strasburg | Apr 16 | Oct 22 | 189 d | 6b |
| Strawn | Apr 21 | Oct 17 | 179 d | 6a |
| Streamwood | Apr 30 | Oct 13 | 166 d | 5b |
| Streator | Apr 12 | Oct 28 | 199 d | 5b |
| Stronghurst | Apr 18 | Oct 20 | 185 d | 6a |
| Sublette | Apr 27 | Oct 12 | 168 d | 5b |
| Sugar Grove | Apr 28 | Oct 13 | 168 d | 5b |
| Sullivan | Apr 15 | Oct 22 | 190 d | 6a |
| Summerfield | Apr 12 | Oct 20 | 191 d | 6b |
| Summit Argo | Apr 11 | Oct 31 | 203 d | 6a |
| Sumner | Apr 12 | Oct 25 | 196 d | 6b |
| Sutter | Apr 10 | Oct 27 | 200 d | 6a |
| Sycamore | Apr 24 | Oct 18 | 177 d | 5b |