Ottawa, IL Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Ottawa, a city in Lasalle County, Illinois.
This Afternoon
70°F
Rain Likely
Rain likely and a slight chance of thunderstorms. Mostly cloudy. High near 70, with temperatures falling to around 67 in the afternoon. South wind 15 to 20 mph, with gusts as high as 35 mph. Chance of precipitation is 70%. New rainfall amounts less than a tenth of an inch possible.
7-day forecast for Ottawa
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| This Afternoon | 70°F | Rain Likely | 15 to 20 mph S | 68% |
| Tonight | 58°F | Rain | 10 to 15 mph S | 92% |
| Wednesday | 61°F | Chance Rain then Mostly Cloudy | 15 mph SSW | 38% |
| Wednesday Night | 47°F | Mostly Cloudy | 10 mph SW | 11% |
| Thursday | 58°F | Mostly Cloudy then Chance Rain | 10 to 15 mph WSW | 35% |
| Thursday Night | 44°F | Chance Rain | 5 mph NW | 36% |
| Friday | 53°F | Slight Chance Rain | 10 mph N | 22% |
| Friday Night | 36°F | Partly Cloudy | 0 to 5 mph NNW | 3% |
| Saturday | 52°F | Mostly Sunny | 0 to 5 mph WNW | 3% |
| Saturday Night | 36°F | Partly Cloudy | 0 mph | 3% |
| Sunday | 58°F | Mostly Sunny | 0 to 5 mph W | 13% |
| Sunday Night | 36°F | Mostly Clear | 0 to 5 mph W | 5% |
| Monday | 62°F | Sunny | 0 to 10 mph WSW | 3% |
| Monday Night | 41°F | Mostly Clear | 5 mph WSW | 1% |
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
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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 Nov 4, 2026.