Illinois weather in August 2026

The temperatures in Illinois in August are comfortable with low of 19°C and and high up to 27°C.

You can expect about 3 to 8 days of rain in Illinois during the month of August. It’s a good idea to bring along your umbrella so that you don’t get caught in poor weather.

Our weather forecast can give you a great sense of what weather to expect in Illinois in August 2026.

If you’re planning to visit Illinois in the near future, we highly recommend that you review the 14 day weather forecast for Illinois before you arrive.

Temperatures

27° / 19°

Rainy Days

Snowy Days

Dry Days

Rainfall

100

Sun Hours

11.1

Hrs

Sun	Mon	Tue	Wed	Thu	Fri	Sat
						1 26° /20°
2 26° /20°	3 27° /21°	4 25° /20°	5 27° /20°	6 25° /20°	7 27° /21°	8 28° /21°
9 27° /20°	10 27° /20°	11 27° /21°	12 27° /21°	13 26° /20°	14 25° /20°	15 25° /20°
16 27° /20°	17 25° /20°	18 25° /20°	19 26° /20°	20 27° /21°	21 25° /19°	22 25° /20°
23 28° /20°	24 28° /19°	25 27° /20°	26 27° /20°	27 28° /20°	28 26° /20°	29 26° /20°
30 24° /19°	31 24° /18°

Explore the weather in Illinois in other months

Illinois annual weather

Month	Temperatures	Rainy Days	Dry Days	Snowy Days	Rainfall	Weather	More details
January	-2° / -7°	5	11	15	39 mm	Awful	Illinois in January
February	0° / -6°	4	11	14	41 mm	Awful	Illinois in February
March	7° / 1°	6	19	6	55 mm	Bad	Illinois in March
April	12° / 5°	7	21	3	79 mm	Awful	Illinois in April
May	19° / 12°	7	24	0	98 mm	Ok	Illinois in May
June	24° / 17°	7	23	0	128 mm	Good	Illinois in June
July	27° / 20°	7	24	0	114 mm	Good	Illinois in July
August	27° / 19°	5	26	0	100 mm	Perfect	Illinois in August
September	24° / 16°	4	26	0	64 mm	Perfect	Illinois in September
October	16° / 10°	5	25	0	65 mm	Good	Illinois in October
November	9° / 3°	4	22	4	40 mm	Bad	Illinois in November
December	3° / -2°	5	16	10	38 mm	Awful	Illinois in December