Cook County Power Outage History
2014–2025 · Illinois
Better than average — fewer or shorter outages than most counties. How grades are calculated
Outages by year
Outages by month (seasonality)
Worst outage events on record
| Date | Duration | Customers affected | Cause |
|---|---|---|---|
| Aug 10, 2020 | 13 hrs | 279,858 (12%) | Thunderstorm Wind |
| Aug 11, 2020 | 11 hrs | 200,977 (8%) | Thunderstorm Wind |
| Aug 11, 2020 | 43 hrs | 163,464 (7%) | Thunderstorm Wind |
| Jul 15, 2024 | 139 hrs | 155,204 (6%) | Flash Flood |
| Mar 13, 2015 | 0 hrs | 144,538 (6%) | Unnamed event |
Over the 12 years from 2014 to 2025, Cook County recorded 11,898 distinct power outage events, averaging 2.3 hours per event.
The single worst outage on record in Cook County started August 10, 2020 (Thunderstorm Wind), lasting 13 hours and leaving up to 279,858 customers without power (12% of the county) at its peak.
June has historically been the worst month for outages in Cook County, with 1,351 events recorded during that month across the dataset.
Based on this history, Cook County earns a Reliability Grade of B, placing it in the 79th percentile nationally for grid reliability (higher percentile = more reliable).
Sized for Cook County's outage profile
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Outage-prep kit
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Similar counties in Illinois
Counties with the closest reliability grade and national percentile to Cook County.
| County | Grade | National percentile |
|---|---|---|
| Kane County | B | 79th |
| Champaign County | B | 79th |
| Henry County | B | 78th |
| Montgomery County | A | 80th |
| DuPage County | A | 80th |
FAQ
How often does power go out in Cook County?
Between 2014 and 2025, Cook County recorded 11,898 outage events, averaging 2.3 hours each.
What is Cook County's reliability grade?
Cook County has a Reliability Grade of B, in the 79th national percentile.
What was the worst power outage in Cook County?
The worst outage on record started August 10, 2020 (Thunderstorm Wind), lasting 13 hours and affecting up to 279,858 customers.