Illinois heat

Every recorded heat record since 1996 · 102 counties with a record

NOAA's Storm Events Database records 3,276 heat records in Illinois from 1996 through June 30, 2026, about 112 a year since 2000. The deadliest was the July 28, 1999 heat in Cook County: 99 deaths across 3 records. Illinois ranks 4th of 51 states and territories by count and 5th of 50 per square mile.

Heat in Illinois, 1996 to 2026

Heat records per year (NOAA Storm Events); 2026 to June 30, 2026.

recorded, no damage figure
under $1 million
$1 million or more
$10 million or more
$100 million or more, or 10 deaths
$1 billion or more, or 100 deaths
a year's colour: its recorded damage or deaths
a year with a death

Records: 3,2761996 to June 30, 2026
A year since 2000: 112average
Deaths: 425444 injuries
Damage, 2025 dollars: $996Kas filed
Busiest year: 2011274 records

Source: NOAA NCEI Storm Events Database, records through June 30, 2026; deaths and damage as filed, damage in 2025 dollars. Search the record at NCEI.

Are heat records common in Illinois?

Illinois averages about 112 heat records a year since 2000, 4th of 51 states and territories by count. The busiest year on record was 2011 (274). Per 10,000 square miles of land, Illinois records 590 heat records since 1996, 5th of 50 states and territories by that measure.

Source: NOAA NCEI Storm Events Database, records since 1996, per 10,000 square miles of land area (Census Bureau 2024 Gazetteer; places under 1,000 square miles not ranked). Damage colours: Storm Events damage, 2025 dollars.

Which counties in Illinois have the most heat records?

Per square mile, Hardin County leads Illinois: 82 days with a heat record since 1996, 462.3 per 1,000 square miles of land. By raw count, Union County has the most heat records (124 since 1996); large counties collect more records simply by covering more ground, so the ranking counts days with a record per unit of area (a storm filed for several forecast zones adds several records but one day).

Hardin County 462.3 (82)
Pulaski County 451.7 (90)
Alexander County 386.6 (91)
Massac County 354.2 (84)
Edwards County 337.2 (105)
Wabash County 335.8 (75)
Gallatin County 263.2 (85)
Johnson County 250.2 (86)
Pope County 225.0 (83)
Union County 225.0 (124)
Saline County 223.7 (117)
Williamson County 211.8 (89)

Source: NOAA NCEI Storm Events Database, days with a record in the county since 1996 per 1,000 square miles of land (Census Bureau 2024 Gazetteer); in brackets, the count of records.

When is the heat season in Illinois?

82% of its heat records since 1996 fell in July and August. The busiest month is July (1,723 records).

The values, month by month

Jan 1 · Feb 19 · Mar 0 · Apr 0 · May 6 · Jun 514 · Jul 1,723 · Aug 948 · Sep 46 · Oct 0 · Nov 0 · Dec 19 (records).

Source: NOAA NCEI Storm Events Database, records by the month they began, since 1996.

What were the deadliest heat records in Illinois?

Illinois: the storms with the most deaths since 1996
Date	Record	Killed	Damage
1999-07-28	HeatCook County · forecast zone Cook One storm episode: 3 records in 3 places; the totals are the episode's. An intense heat wave began in the Chicago metropolitan area July 28th and continued through the morning of July 31st. High temperatures on the 28th were in the lower to middle 90s with heat indices 100 to 105. On the 29th the temperatures soared to the middle and upper 90s with heat indices 110 to 120. The heat peaked ...	99	–
2012-07-04	Excessive HeatCook County · forecast zone Cook Northern Illinois experienced an intense heat wave during the first week of July. High temperatures at Chicago O'Hare Airport reached 102 on the 4th, 103 on the 5th and 6th and 98 on the 7th. Low temperatures remained in the upper 70s to lower 80s during much of the heat wave with a low temperature of just 82 degrees ...	25	$964K
2006-08-01	HeatCook County · forecast zone Cook The second heat wave of the summer developed during late July 2006 and continued into early August. See Stormdata, July 2006, Illinois, Northeast. The high temperature at Northerly Island in downtown Chicago reached 99 on August 1st and 96 on August 2nd. The peak heat reached 115 on August 1st and 114 on August 2nd. ...	24	–
2011-07-17	HeatCook County · forecast zone Cook The Chicago area experienced an intense heat wave in mid to late July. High temperatures at Chicago O'Hare were 95 on the 17th, 92 on the 18th, 93 on the 19th, 99 on the 20th, and 99 on the 21st. Low temperatures were mostly in the 70s. Thunderstorms brought some relief on the 22nd and 23rd but temperatures remained ...	16	–
1997-06-21	HeatCook County · forecast zone Cook From the period of June 21st through June 30th, temperatures were in the middle 80s to lower 90s, causing heat-related deaths throughout the Chicago area.	16	–
2001-08-06	HeatCook County · forecast zone Cook The high temperature climbed to 92 degrees at Ohare Airport on August 6th with a maximum heat index of 93 degrees. Heat indices arond the Chicago metro area were in the middle 90s. On August 7th, the high temperature was 95 at Ohare Airport with a heat index of 105 degrees, maximum heat indices around the metro area ...	14	–
1999-07-21	HeatCook County · forecast zone Cook One storm episode: 2 records in 2 places; the totals are the episode's. A moderate heat wave began in the Chicago metropolitan area on July 21 and continued through July 25. A weak lake breeze moderated temperatures along the immediate lakefront on the 21st and 22nd, but the intense heat spread inland through the entire metro area on the 23rd through the 25th. Daily high temperatures were ...	13	–
2002-07-01	HeatCook County · forecast zone Cook July 2002 began well above normal with high temperatures in the lower to middle 90s across the Chicago area with overnight low temperatures mainly in the 70s. The prolonged heat and humidity which began in late June 2002, caused several heat related fatalities in Cook county.	12	–
2002-07-15	HeatCook County · forecast zone Cook An extended period of hot weather began on July 15th and continued through July 22nd. High temperatures ranged mainly from the upper 80s to middle 90s. July 21st was the hottest day when high temperatures reached the middle to upper 90s. Ohare Airport reported their highest temperature of the month, 96 degrees on July ...	11	–
1998-06-24	HeatCook County · forecast zone Cook Daytime temperatures were in the lower to middle 90s with dewpoints in the 70s on the 24th and 25th, producing heat indices of 102 to 107. Thunderstorms brought some relief from the heat on the 26th, though humidity was still high. The heat reurned on the 27th with a peak heat index of 107. The 28th was a little ...	10	–

Source: NOAA NCEI Storm Events Database: deaths direct and indirect, as filed by the National Weather Service, summed over each storm (one episode, or one named storm filed by several offices). Storm names from the titles of FEMA declarations that name the storm's counties.

The costliest heat records in Illinois

Illinois: the most damaging storms since 1993, 2025 dollars
Date	Record	Character	Killed	Injured	Damage
2012-07-04	Excessive HeatCook County · forecast zone Cook		25	0	$964K
2013-07-19	Excessive HeatCook County · forecast zone Cook One storm episode: 3 records in 2 places; the totals are the episode's.		6	0	$32K

Source: NOAA NCEI Storm Events Database: property and crop damage as estimated by the National Weather Service, in 2025 dollars.

Are heat records becoming more frequent in Illinois?

Illinois's count per decade against the whole country's, and its share. NOAA recorded every event type only from 1996, so earlier decades are not comparable; the share of the national total is the fairer comparison across decades.

Heat: Illinois and the United States by decade (2020s to June 30, 2026)
Decade	Illinois	United States	Illinois's share
1996-99	330	4,355	7.6%
2000s	704	9,163	7.7%
2010s	1,437	16,445	8.7%
2020-26	805	26,796	3.0%

Source: NOAA NCEI Storm Events Database.

The most recent heat records in Illinois

The 12 most recent records, to June 30, 2026
Date	Record	Damage
2026-06-29	Excessive HeatCook County · forecast zone Southern Cook County	–
2026-06-29	Excessive HeatCook County · forecast zone Central Cook County	–
2026-06-29	Excessive HeatCook County · forecast zone Northern Cook County	–
2026-06-29	HeatIroquois County · forecast zone Iroquois	–
2026-06-29	HeatFord County · forecast zone Ford	–
2026-06-29	HeatKankakee County · forecast zone Kankakee	–
2026-06-29	HeatLivingston County · forecast zone Livingston	–
2026-06-29	HeatWill County · forecast zone Eastern Will County	–
2026-06-29	HeatWill County · forecast zone Southern Will County	–
2026-06-29	HeatWill County · forecast zone Northern Will County	–
2026-06-29	HeatGrundy County · forecast zone Grundy	–
2026-06-29	HeatKendall County · forecast zone Kendall	–

Source: NOAA NCEI Storm Events Database, records through June 30, 2026; the newest months are revised by NCEI as reports arrive. Search the record at NCEI.