A 16th person in the Chicago area has died of heat-related causes.
The Cook County medical examiner's office listed heat stroke and hypertension as the causes of death for 70-year-old William Blackledge of Chicago on Wednesday.
Heat has been a factor in 15 other Cook County deaths in the last two weeks as temperatures have soared into the 90s.
The last similar heat wave in the region in 1995 resulted in more than 750 deaths over a five-day period.
The heat has claimed several other people statewide, many of whom ranged in age from their 70s to 90s.
Authorities say some of those who died had working air-conditioners but didn't have them on.
Investigators say temperatures inside several homes were well above 110 degrees.