News Updates

New regional data to help northeastern Illinois target areas for resilience support

Extreme heat may not get the same attention as a flood, but it’s often the deadliest weather-related hazard in the United States each year. As the climate continues to warm, the number of extremely hot days in northeastern Illinois could increase from a historical average of 2 days per year to up to 45 days by 2100. More frequent extreme heat — combined with more humid nights — poses serious health risks, from dehydration and heat exhaustion to life-threatening heat stroke.

While heat affects everyone differently, there are areas where heat risk is more concentrated than others. The Chicago Metropolitan Agency for Planning (CMAP) created the Heat Vulnerability Index (HVI) to identify higher-risk areas so communities can focus their planning and mitigation activities.

The HVI scores census tracts on a scale of 1 to 10 based on factors that increase the likelihood of heat-related health impacts. The higher an area’s ranking, the more likely its residents will experience heat-related health risks. Because it’s static, the HVI reflects risk based on where people live, not where they travel or how they cope during a heat wave. While some areas show greater vulnerability for residents, it’s important to note that people can experience heat-related risks anywhere.

Key findings

Much of the region faces high or very high vulnerability

Nearly half of the region (44 percent) lives in census tracts with HVI score of 5.7/10 or above, putting a lot of the population at risk.

The central and southwest portions of the region have the highest vulnerability

Parts of Cook, Kane, Kendall, and Will counties have the greatest heat vulnerability, spanning some of northeastern Illinois’ most urban and more rural communities.

Surface temperature and tree cover drive vulnerability in Cook, Kendall, and Will counties

In Cook County, extensive impervious surfaces intensify the urban heat island effect. In Kendall and Will counties, intensive agriculture limits tree cover, which reduces natural cooling and increases surface temperatures.

Advanced age and health conditions increase vulnerability in DuPage, Kane, Kendall, and McHenry counties

These counties have larger populations of residents 65 and older and higher rates of health conditions such as diabetes, asthma, coronary disease, and other related conditions and disabilities. This increases sensitivity to extreme heat and the risk of heat-related illness.

Communities with more tree canopy are less vulnerable

Trees cool surrounding areas by providing shade and releasing water vapor. For example, despite having a relatively large share of older adults and residents with health risks, Lake County has the lowest average vulnerability score in the region, in part due to its expansive tree canopy.

How is the HVI created?

The HVI uses a combination of heat exposure, sensitivity, and adaptability data to determine overall vulnerability on a scale of 1 (less vulnerable) to 10 (most vulnerable). Some of the data used includes tree canopy coverage, summer surface temperature, number of people younger than 5 or older than 64, and estimates of people with asthma, diabetes, or experiencing poverty. The methodology report includes more details on the data inputs and analysis.

How can the region use the HVI?

This data is a valuable resource to communicate the region’s growing extreme heat challenge and to support planning and resilience activities for communities facing higher vulnerability. It complements other efforts, such as the City of Chicago’s heat vulnerability index (currently in development) and CMAP’s analysis of transit rider vulnerability to extreme heat. It can also be used alongside other datasets — such as land use, building age, access to air conditioning, or climate projections — to support more coordinated and data-driven decisions across the region.

CMAP encourages community planners and other stakeholders to use the index to:

• Screen for extreme heat risk when developing comprehensive, corridor, and other local plans to identify who is most vulnerable and where heat resilience strategies are needed most.
• Engage communities to help communicate risk, verify the data, and gather local insights to inform planning and investment decisions.
• Prioritize heat resilience investments, including shade trees and structures, drinking water fountains, cooling centers, building retrofits, and green infrastructure.

Download the 2026 HVI data from CMAP’s Data Hub or view it through an interactive web map. You can learn more about the methodology in the 2026 HVI report.