Montana frost dates: C
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Cameron | Jun 16 | Sep 4 | 80 d | 5a |
| Canyon Creek | Jun 4 | Sep 14 | 102 d | 4b |
| Capitol | May 17 | Sep 24 | 130 d | 4b |
| Cardwell | May 9 | Sep 27 | 141 d | 5a |
| Carter | May 23 | Sep 23 | 123 d | 4a |
| Cascade | May 21 | Sep 19 | 121 d | 4b |
| Charlo | May 12 | Oct 2 | 143 d | 6a |
| Chester | May 24 | Sep 17 | 116 d | 4a |
| Chinook | May 14 | Sep 23 | 132 d | 3b |
| Choteau | May 28 | Sep 12 | 107 d | 4b |
| Circle | May 17 | Sep 22 | 128 d | 4a |
| Clancy | Jun 18 | Sep 5 | 79 d | 4b |
| Clinton | frost any month | 5b | ||
| Clyde Park | Jun 4 | Sep 6 | 94 d | 5a |
| Coffee Creek | Jun 1 | Sep 11 | 102 d | 4b |
| Cohagen | May 25 | Sep 14 | 112 d | 4a |
| Colstrip | May 15 | Sep 30 | 138 d | 5a |
| Columbia Falls | May 31 | Sep 10 | 102 d | 5a |
| Columbus | May 27 | Sep 14 | 110 d | 5a |
| Condon | May 20 | Sep 22 | 125 d | 5a |
| Conner | frost any month | 5b | ||
| Conrad | May 20 | Sep 19 | 122 d | 4a |
| Cooke City | frost any month | 4b | ||
| Coram | May 18 | Sep 20 | 125 d | 5a |
| Corvallis | May 23 | Sep 21 | 121 d | 5b |
| Crane | May 12 | Sep 25 | 136 d | 4a |
| Crow Agency | May 13 | Sep 29 | 139 d | 4b |
| Culbertson | May 21 | Sep 20 | 122 d | 4a |
| Custer | May 22 | Sep 22 | 123 d | 4b |
| Cut Bank | May 24 | Sep 15 | 114 d | 4a |