Ottawa, IL Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Ottawa, a city in Lasalle County, Illinois.
This Afternoon
75°F
Showers And Thunderstorms Likely
Showers and thunderstorms likely. Partly sunny, with a high near 75. East wind around 10 mph, with gusts as high as 20 mph. Chance of precipitation is 60%. New rainfall amounts less than a tenth of an inch possible.
7-day forecast for Ottawa
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| This Afternoon | 75°F | Showers And Thunderstorms Likely | 10 mph E | 57% |
| Tonight | 66°F | Mostly Cloudy then Chance Showers And Thunderstorms | 10 mph ESE | 28% |
| Saturday | 82°F | Showers And Thunderstorms Likely | 5 to 10 mph SE | 63% |
| Saturday Night | 67°F | Showers And Thunderstorms Likely | 5 mph NNW | 79% |
| Sunday | 71°F | Showers And Thunderstorms | 5 to 15 mph NE | 79% |
| Sunday Night | 58°F | Showers And Thunderstorms Likely | 15 mph NE | 72% |
| Monday | 66°F | Showers And Thunderstorms Likely | 15 mph ENE | 61% |
| Monday Night | 54°F | Chance Rain Showers | 10 to 15 mph NE | 34% |
| Tuesday | 64°F | Chance Rain Showers | 10 mph NE | 26% |
| Tuesday Night | 53°F | Mostly Cloudy | 5 to 10 mph NNE | 9% |
| Wednesday | 68°F | Partly Sunny | 5 to 10 mph NNE | 5% |
| Wednesday Night | 53°F | Partly Cloudy | 0 to 5 mph NNE | 4% |
| Thursday | 69°F | Mostly Sunny | 5 mph N | 2% |
| Thursday Night | 55°F | Partly Cloudy | 0 to 5 mph NNE | 3% |
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 Sep 18, 2026.