select pnm,lnm,st_cd,st_nm,cnty_id,dm,dm_date,dm_hist,avg_tmax_data,avg_tmin_data,avg_prcp_data,rec_hi_data,rec_lo_data,avg_sndp_data,x,y,ff,lf,fd,hz,er,hz_source,kg,hzd,clim_stn_nm,hz12,hz90, feels_like_min,feels_like_max,days_of_prcp,snow,cloud_cover,humidity,wind_speed from worldtg8_pm.pm_climate_points_namer where surl = 'grand-detour' and st_surl='illinois' and iso_cc = 'US' and prim_loc in (1,2) Grand Detour Illinois Climate Data - Updated February 2026

Grand Detour Illinois Climate Data

Monthly Average Climate Data for Grand Detour Illinois

Switch Data to Celsius/Metric Units

Month	Avg. Low	Avg. High	Avg. Precip
January	12.7 °F	29.1 °F	1.77 in.
February	16.4 °F	33.7 °F	1.76 in.
March	27.1 °F	46.3 °F	2.44 in.
April	37.6 °F	59.8 °F	3.68 in.
May	49.5 °F	71.0 °F	4.82 in.
June	59.3 °F	79.9 °F	5.16 in.
July	62.6 °F	82.7 °F	4.36 in.
August	60.6 °F	81.2 °F	4.03 in.
September	52.3 °F	75.4 °F	3.64 in.
October	40.6 °F	62.5 °F	2.9 in.
November	29.6 °F	47.4 °F	2.33 in.
December	19.3 °F	34.8 °F	2.04 in.
Annual	39 °F	58.7 °F	38.93 in.

Climate Data for Grand Detour Illinois

Average First Frost Date	Oct. 11 - Oct. 20
Average Last Frost Date	Apr. 21 - Apr. 30
Average Days With Frost	100-125 Days
Plant Hardiness Zone	Zone 5b : -15°F to -10°F
Plant Hardiness Zone - 2012	Zone 5a : -20°F to -15°F
Current Drought Conditions	Abnormally Dry
Köppen Climate Classification	Dfa - Humid Continental Hot Summers With Year Around Precipitation

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