Illinois frost dates: R
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Radom | Apr 7 | Oct 26 | 202 d | 6b |
| Raleigh | Apr 7 | Oct 26 | 202 d | 7a |
| Ramsey | Apr 15 | Oct 19 | 187 d | 6b |
| Rankin | Apr 22 | Oct 19 | 180 d | 6a |
| Ransom | Apr 12 | Oct 28 | 199 d | 5b |
| Rantoul | Apr 21 | Oct 18 | 180 d | 6a |
| Rapids City | Apr 16 | Oct 25 | 192 d | 5b |
| Raritan | Apr 21 | Oct 19 | 181 d | 5b |
| Raymond | Apr 12 | Oct 20 | 191 d | 6b |
| Red Bud | Apr 8 | Oct 30 | 205 d | 7a |
| Reddick | Apr 27 | Oct 15 | 171 d | 5b |
| Redmon | Apr 21 | Oct 20 | 182 d | 6a |
| Renault | Apr 9 | Oct 26 | 200 d | 7a |
| Reynolds | Apr 22 | Oct 19 | 180 d | 5b |
| Richmond | Apr 30 | Oct 13 | 166 d | 5b |
| Richton Park | Apr 23 | Oct 20 | 180 d | 6a |
| Richview | Apr 7 | Oct 26 | 202 d | 6b |
| Ridge Farm | Apr 19 | Oct 19 | 183 d | 6a |
| Ridgway | Apr 5 | Oct 31 | 209 d | 7a |
| Ridott | Apr 26 | Oct 13 | 170 d | 5b |
| Rinard | Apr 9 | Oct 24 | 198 d | 6b |
| Ringwood | May 1 | Oct 11 | 163 d | 5b |
| Rio | Apr 20 | Oct 19 | 182 d | 5b |
| River Forest | Apr 11 | Oct 31 | 203 d | 6a |
| River Grove | Apr 16 | Oct 28 | 195 d | 6a |
| Riverdale | Apr 10 | Nov 1 | 205 d | 6a |
| Riverside | Apr 11 | Oct 31 | 203 d | 6a |
| Riverton | Apr 14 | Oct 20 | 189 d | 6a |
| Roanoke | Apr 26 | Oct 17 | 174 d | 5b |
| Robbins | Apr 10 | Nov 1 | 205 d | 6a |
| Roberts | Apr 25 | Oct 20 | 178 d | 6a |
| Robinson | Apr 13 | Oct 22 | 192 d | 6b |
| Rochelle | Apr 26 | Oct 13 | 170 d | 5b |
| Rochester | Apr 15 | Oct 22 | 190 d | 6a |
| Rock City | Apr 26 | Oct 13 | 170 d | 5a |
| Rock Falls | Apr 21 | Oct 19 | 181 d | 5b |
| Rock Island | Apr 19 | Oct 22 | 186 d | 5b |
| Rockbridge | Apr 13 | Oct 22 | 192 d | 6b |
| Rockford | Apr 24 | Oct 17 | 176 d | 5b |
| Rockport | Apr 14 | Oct 21 | 190 d | 6b |
| Rockton | May 1 | Oct 12 | 164 d | 5b |
| Rockwood | Apr 19 | Oct 20 | 184 d | 7a |
| Rolling Meadows | Apr 19 | Oct 26 | 190 d | 6a |
| Rome | Apr 20 | Oct 17 | 180 d | 6a |
| Romeoville | Apr 20 | Oct 22 | 185 d | 6a |
| Roodhouse | Apr 13 | Oct 22 | 192 d | 6a |
| Rosamond | Apr 17 | Oct 23 | 189 d | 6b |
| Roscoe | May 1 | Oct 12 | 164 d | 5b |
| Roselle | Apr 30 | Oct 13 | 166 d | 5b |
| Roseville | Apr 22 | Oct 19 | 180 d | 5b |
| Rosiclare | Apr 19 | Oct 20 | 184 d | 7a |
| Rossville | Apr 22 | Oct 19 | 180 d | 6a |
| Round Lake | Apr 24 | Oct 23 | 182 d | 5b |
| Roxana | Apr 4 | Nov 5 | 215 d | 7a |
| Royal | Apr 20 | Oct 21 | 184 d | 6a |
| Royalton | Apr 6 | Oct 22 | 199 d | 7a |
| Rushville | Apr 16 | Oct 23 | 190 d | 6a |
| Russell | Apr 30 | Oct 21 | 174 d | 5b |
| Rutland | Apr 26 | Oct 17 | 174 d | 5b |