Illinois frost dates: U
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Ullin | Apr 3 | Nov 5 | 216 d | 7a |
| Union | Apr 28 | Oct 12 | 167 d | 5b |
| Union Hill | Apr 19 | Oct 24 | 188 d | 5b |
| Unity | Apr 2 | Oct 31 | 212 d | 7a |
| University Park | Apr 23 | Oct 20 | 180 d | 6a |
| Urbana | Apr 15 | Oct 24 | 192 d | 6a |
| Ursa | Apr 11 | Oct 23 | 195 d | 6a |
| Utica | Apr 20 | Oct 22 | 185 d | 5b |