Mayor Rahm Emanuel wants an explanation of the city's response during three consecutive days of triple-digit heat.
Emanuel ordered a report due in 60 days from the Chicago Office of Emergency Management detailing how resources were used and what can be done to use them better.
The mayor's request came as the Cook County Medical Examiner's Office confirmed 18 people died from heat-related causes.
Autopsies performed Friday found heat stress coupled with heart disease factored into the deaths of six people Thursday. Four more died Friday, including a 53-year-old man, a 65-year-old woman, an unidentified man believed to be in his 30s and a 46-year-old woman.
The medical examiner's office confirmed eight more people died over the weekend from heat-related causes before 100-degree temperatures broke. One of the victims, Lucille Griffith, was 100 years old. She died from a combination of heart disease and heat stress.
This isn't the first time Emanuel ordered an extreme weather report.
Before his administration was in place, he requested a formal report of city performance during the Blizzard of 2011. Then-candidate Emanuel criticized city response as the blizzard crippled the city and shut down Lake Shore Drive with hundreds of cars still on it.
Emanuel got his report, resulting in multiple recommendations and extreme-weather changes.