WhenToBird

Ardea herodias · Ardeidae

When Do Great Blue Herons Arrive in Illinois?

Adult Great Blue Heron
Photo: mostbittern, CC BY 4.0 via iNaturalist

Great Blue Herons are in Illinois all year, but most are here in summer: numbers build from early April, peak in the second week of August (33% of checklists), and fall back by mid October. In the quietest week (mid February) they are still on about 4.7% of checklists.

When to look

Numbers buildApr 1-7early April
PeakAug 8-14the second week of August
Fall back byOct 15-21mid October
FewestFeb 15-21mid February

Best: the second week of August. Here all year; numbers build from early April and fall back by mid October. Peak: on about 33% of Illinois checklists.

  1. Januncommon
  2. Febuncommon
  3. Marcommon
  4. Aprcommon
  5. Maycommon
  6. Juncommon
  7. Julpeak season
  8. Augpeak season
  9. Seppeak season
  10. Octpeak season
  11. Novcommon
  12. Decuncommon

Darker months: more checklists report it. Outlined: peak month.

0%10%20%30%40%Jan 1-7: 7.1% of 29700 checklistsJan 8-14: 6.1% of 20189 checklistsJan 15-21: 5.8% of 19784 checklistsJan 22-31: 6.0% of 26641 checklistsFeb 1-7: 5.9% of 20478 checklistsFeb 8-14: 4.6% of 21967 checklistsFeb 15-21: 4.0% of 28735 checklistsFeb 22-28: 5.6% of 24223 checklistsMar 1-7: 6.3% of 26775 checklistsMar 8-14: 8.9% of 27579 checklistsMar 15-21: 13% of 27193 checklistsMar 22-31: 18% of 42278 checklistsApr 1-7: 19% of 34579 checklistsApr 8-14: 20% of 38290 checklistsApr 15-21: 21% of 39261 checklistsApr 22-30: 22% of 59584 checklistsMay 1-7: 22% of 60485 checklistsMay 8-14: 23% of 59647 checklistsMay 15-21: 24% of 43173 checklistsMay 22-31: 24% of 47913 checklistsJun 1-7: 21% of 31151 checklistsJun 8-14: 21% of 27692 checklistsJun 15-21: 21% of 23983 checklistsJun 22-30: 22% of 28448 checklistsJul 1-7: 26% of 21273 checklistsJul 8-14: 28% of 19284 checklistsJul 15-21: 30% of 17712 checklistsJul 22-31: 31% of 24500 checklistsAug 1-7: 32% of 18498 checklistsAug 8-14: 34% of 19331 checklistsAug 15-21: 32% of 19983 checklistsAug 22-31: 29% of 31892 checklistsSep 1-7: 28% of 26396 checklistsSep 8-14: 26% of 25011 checklistsSep 15-21: 26% of 23597 checklistsSep 22-30: 27% of 30638 checklistsOct 1-7: 25% of 23949 checklistsOct 8-14: 23% of 24412 checklistsOct 15-21: 20% of 22359 checklistsOct 22-31: 18% of 29794 checklistsNov 1-7: 16% of 21877 checklistsNov 8-14: 13% of 19742 checklistsNov 15-21: 12% of 18989 checklistsNov 22-30: 11% of 23905 checklistsDec 1-7: 9.7% of 16935 checklistsDec 8-14: 9.0% of 16687 checklistsDec 15-21: 8.9% of 20931 checklistsDec 22-31: 7.8% of 29011 checklistsJanFebMarAprMayJunJulAugSepOctNovDec
Share of complete checklists reporting it, by week (4 per month). Grey bars: fewer than 10 checklists, not counted.

Frequency is the share of complete checklists in Illinois that listed the bird, 2016–2025. It is not a head count, and it follows where and when people go birding. How to read it.

JanFebMarAprMayJunJulAugSepOctNovDec
today
Second week of November

Each county is shaded by the share of complete checklists there that listed the bird, blended with the weeks either side. Darker is more often. It follows where people watch birds, not how many birds there are. How to read it.

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Where in Illinois

Best counties

Share of checklists at the peak
  1. Wayne CountyBest late September · 12 checklists that week, 394 in all83%
  2. Alexander CountyBest the second week of September · 19 checklists that week, 2,108 in all78%
  3. Moultrie CountyBest late August · 53 checklists that week, 1,367 in all77%
  4. Jasper CountyBest late July · 13 checklists that week, 1,292 in all77%
  5. Calhoun CountyBest early August · 11 checklists that week, 786 in all76%
  6. Franklin CountyBest the second week of October · 28 checklists that week, 1,745 in all75%

Best spots

Share of checklists at the peak
  1. Carbondale ReservoirJackson County, best the second week of August · 28 checklists that week, 1,735 in all99%
  2. Lake RenwickWill County, best early April · 20 checklists that week, 582 in all99%
  3. Nippersink 1 (Round Lake)Lake County, best mid August · 22 checklists that week, 152 in all98%

Busy spots report more of everything; compare the checklist counts before you drive anywhere.

Best time of day

In Illinois, the Great Blue Heron is most often listed on checklists started between 6 and 8 am (22% of those checklists).

0%10%20%30%12 am: too few checklists (484) to judge1 am: too few checklists (631) to judge2 am: too few checklists (485) to judge3 am: too few checklists (610) to judge4 am: too few checklists (2321) to judge5 am: too few checklists (23536) to judge6 am: 23% of 95511 checklists7 am: 22% of 164584 checklists8 am: 20% of 163654 checklists9 am: 19% of 141804 checklists10 am: 18% of 122882 checklists11 am: 17% of 100640 checklists12 pm: 16% of 89894 checklists1 pm: 16% of 82729 checklists2 pm: 17% of 79801 checklists3 pm: 16% of 82169 checklists4 pm: 17% of 75124 checklists5 pm: 20% of 57708 checklists6 pm: 21% of 41843 checklists7 pm: too few checklists (20943) to judge8 pm: too few checklists (6131) to judge9 pm: too few checklists (1677) to judge10 pm: too few checklists (843) to judge11 pm: too few checklists (448) to judge12a3a6a9a12p3p6p9p
Share of checklists started in each local hour that reported it. It reflects when people go birding as well as when birds are active. Grey hours have too few checklists (under 2% of the state’s, or under 200) to judge.
Week-by-week table
MonthDays 1-78-1415-2122-end
January7.1%6.1%5.8%6.0%
February5.9%4.6%4.0%5.6%
March6.3%8.9%13%18%
April19%20%21%22%
May22%23%24%24%
June21%21%21%22%
July26%28%30%31%
August32%34%32%29%
September28%26%26%27%
October25%23%20%18%
November16%13%12%11%
December9.7%9.0%8.9%7.8%

Neighboring states

  • Indiana: year-round, peaks mid August
  • Wisconsin: arrives the second week of March, 3 weeks earlier than Illinois
  • Michigan: arrives mid April, 2 weeks later than Illinois
  • Iowa: arrives early March, 4 weeks earlier than Illinois

Common questions

When do Great Blue Herons arrive in Illinois?
Great Blue Herons are in Illinois all year, but most are here in summer: numbers build from early April, peak in the second week of August (33% of checklists), and fall back by mid October. In the quietest week (mid February) they are still on about 4.7% of checklists.
When do Great Blue Herons leave Illinois?
Great Blue Herons never fully leave Illinois: numbers fall back below half their usual rate by mid October, but some are still reported in every week, about 4.7% of checklists at the low.
When is the best time to see a Great Blue Heron in Illinois?
The Great Blue Heron is reported most often in the second week of August, on about 33% of Illinois checklists.
Where in Illinois are Great Blue Herons seen most often?
By county, Wayne County, Alexander County, and Moultrie County have the highest peak reporting rates for the Great Blue Heron (counties with at least 200 checklists).