Ottawa, IL Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Ottawa, a city in Lasalle County, Illinois.
Today
85°F
Mostly Sunny
Mostly sunny, with a high near 85. South southwest wind 5 to 10 mph.
7-day forecast for Ottawa
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Today | 85°F | Mostly Sunny | 5 to 10 mph SSW | 0% |
| Tonight | 68°F | Mostly Cloudy then Slight Chance Showers And Thunderstorms | 5 mph S | 17% |
| Wednesday | 81°F | Slight Chance Showers And Thunderstorms | 5 mph SW | 58% |
| Wednesday Night | 66°F | Showers And Thunderstorms | 0 to 5 mph NW | 88% |
| Thursday | 80°F | Chance Showers And Thunderstorms | 0 to 5 mph ESE | 68% |
| Thursday Night | 64°F | Chance Showers And Thunderstorms then Partly Cloudy | 0 to 5 mph SE | 25% |
| Friday | 83°F | Mostly Sunny | 0 to 5 mph SSE | 6% |
| Friday Night | 66°F | Mostly Clear | 0 mph | 9% |
| Saturday | 85°F | Mostly Sunny | 0 to 5 mph SSW | 9% |
| Saturday Night | 71°F | Mostly Clear | 5 mph SSW | 10% |
| Sunday | 87°F | Mostly Sunny | 5 to 10 mph SW | 10% |
| Sunday Night | 71°F | Slight Chance Showers And Thunderstorms | 5 to 10 mph SSW | 29% |
| Monday | 87°F | Chance Showers And Thunderstorms | 5 to 10 mph SSW | 29% |
| Monday Night | 71°F | Chance Showers And Thunderstorms | 5 to 10 mph WSW | 38% |
Forecast source: National Weather Service (api.weather.gov) for Ottawa (41.354, -88.823). Updated through the day.
Growing snapshot for Ottawa
Last spring frost
Apr 20
First fall frost
Oct 22
Growing season
183 days
Hardiness zone
5b
More local growing data for Ottawa: nearby ZIP 61350 weather · frost dates · planting calendar · Illinois frost dates
Nearby towns & communities
Cedar Point
Dana
Dayton
Earlville
Grand Ridge
Harding
Kangley
LaSalle
Leland
Leonore
Lostant
Marseilles
Mendota
Millington
Naplate
Newark
North Utica
Oglesby
Peru
Ransom
Rutland
Seneca
Serena
Sheridan
Streator
Tonica
Triumph
Troy Grove
Wedron
Wenona
Climate data from the nearest NOAA station, Ottawa 5Sw, Il (3.8 mi from Ottawa). Frost dates are 1991–2020 averages, not a forecast. Page updated Aug 4, 2026.