Cortland, IL Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Cortland, a town in Dekalb County, Illinois.
This Afternoon
71°F
Showers And Thunderstorms Likely
Showers and thunderstorms likely. Cloudy, with a high near 71. South southeast wind around 5 mph, with gusts as high as 15 mph. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch possible.
7-day forecast for Cortland
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| This Afternoon | 71°F | Showers And Thunderstorms Likely | 5 mph SSE | 74% |
| Tonight | 63°F | Showers And Thunderstorms | 5 to 10 mph SE | 100% |
| Sunday | 65°F | Showers And Thunderstorms | 10 to 15 mph NE | 84% |
| Sunday Night | 54°F | Slight Chance Rain Showers | 10 to 15 mph ENE | 22% |
| Monday | 63°F | Chance Rain Showers | 15 mph ENE | 44% |
| Monday Night | 50°F | Chance Rain Showers | 10 to 15 mph NE | 44% |
| Tuesday | 61°F | Chance Rain Showers | 10 to 15 mph NE | 44% |
| Tuesday Night | 49°F | Mostly Cloudy | 10 to 15 mph NE | 11% |
| Wednesday | 64°F | Mostly Cloudy | 10 to 15 mph NE | 8% |
| Wednesday Night | 50°F | Mostly Cloudy | 5 to 10 mph NNE | 2% |
| Thursday | 67°F | Partly Sunny | 5 to 10 mph NE | 6% |
| Thursday Night | 52°F | Mostly Cloudy | 0 to 5 mph NE | 10% |
| Friday | 71°F | Partly Sunny | 0 to 5 mph NE | 9% |
| Friday Night | 51°F | Partly Cloudy | 0 to 5 mph NE | 6% |
Forecast source: National Weather Service (api.weather.gov) for Cortland (41.937, -88.689). Updated through the day.
Growing snapshot for Cortland
Last spring frost
Apr 24
First fall frost
Oct 18
Growing season
177 days
Hardiness zone
5b
More local growing data for Cortland: nearby ZIP 60112 weather · frost dates · planting calendar · Illinois frost dates
Nearby towns & communities
DeKalb
Genoa
Hinckley
Kingston
Kirkland
Lake Holiday
Malta
Sandwich
Shabbona
Somonauk
Sycamore
Waterman
Climate data from the nearest NOAA station, De Kalb, Il (4.4 mi from Cortland). Frost dates are 1991–2020 averages, not a forecast. Page updated Sep 19, 2026.