Johnson CountyPower Outage History
What this grade means
(How grades are calculated)Average — typical outage frequency and duration nationally. This county sits in the middle of the national distribution — its outage frequency and duration over the past 12 years are close to the nationwide median, neither notably better nor worse than most other US counties. A typical amount of backup-power preparedness is reasonable here.
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Outages by year
Outages by month (seasonality)
Worst outage events on record
| Date | Duration | Customers affected | Cause |
|---|---|---|---|
| Aug 10, 2020 | 175 hrs | 51,777 (51%) | Thunderstorm Wind |
| Mar 10, 2017 | 2 hrs | 42,670 (42%) | Thunderstorm Wind |
| Jul 9, 2017 | 2 hrs | 18,167 (18%) | Unnamed event |
| Nov 5, 2018 | <1 hr | 12,865 (13%) | Unnamed event |
| Oct 11, 2016 | 2 hrs | 12,594 (12%) | Unnamed event |
Was There an Outage on a Specific Date?
Pick a date to see whether a power outage was recorded for Johnson County, Iowa that day.
Over the 12 years from 2014 to 2025, Johnson County recorded 666 distinct power outage events, averaging 2.1 hours per event.
The single worst outage on record in Johnson County started August 10, 2020 (Thunderstorm Wind), lasting 175 hours and leaving up to 51,777 customers without power (51% of the county) at its peak.
August has historically been the worst month for outages in Johnson County, with 86 events recorded during that month across the dataset.
Based on this history, Johnson County earns a Reliability Grade of C, placing it in the 58th percentile nationally for grid reliability (higher percentile = more reliable).
Similar counties in Iowa
Counties with the closest reliability grade and national percentile to Johnson County.
| County | Grade | National percentile |
|---|---|---|
| Allamakee County | C | 58th |
| Sac County | C | 58th |
| Webster County | C | 59th |
| Butler County | C | 59th |
| Guthrie County | C | 59th |
Most reliable counties nationally
The top 3 counties nationally by reliability grade and percentile.
| County | State | Grade | National percentile |
|---|---|---|---|
| Clay County | South Dakota | A | 100th |
| Clearwater County | Minnesota | A | 99th |
| Limestone County | Alabama | A | 99th |
Least reliable counties nationally
The bottom 3 counties nationally by reliability grade and percentile.
| County | State | Grade | National percentile |
|---|---|---|---|
| Clay County | West Virginia | F | 0th |
| Lincoln County | West Virginia | F | 0th |
| Cameron Parish | Louisiana | F | 0th |
FAQ
How often does power go out in Johnson County?
Between 2014 and 2025, Johnson County recorded 666 outage events, averaging 2.1 hours each.
What is Johnson County's reliability grade?
Johnson County has a Reliability Grade of C, in the 58th national percentile.
What was the worst power outage in Johnson County?
The worst outage on record started August 10, 2020 (Thunderstorm Wind), lasting 175 hours and affecting up to 51,777 customers.