Mosquito season in Calhoun County, IL: when it starts and ends

Mosquito months in Calhoun County

In a normal year mosquito season in Calhoun County, IL starts around April 6 and ends around October 29, about 29 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Calhoun County, and when

• Start tipping out standing water weekly by March 23.
• Book any yard treatment for early April, ahead of the July peak.
• Repellent can go away after October 29.
• No West Nile cases since 2016, so bites in Calhoun County are a nuisance; check window screens.

Calhoun County against the rest of IL

Calhoun County has the 43rd longest season of 102 IL counties, at 206 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 53.9°F.

• Shelby County: April 5 to October 29 (207 days, 0 WNV)
• Jersey County: April 5 to October 28 (206 days, 1 WNV)
• Hardin County: April 6 to October 29 (206 days, 0 WNV)
• Macon County: April 6 to October 28 (205 days, 4 WNV)

West Nile in Calhoun County

CDC ArboNET lists no human West Nile cases for Calhoun County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 6 of those years.

Background: when the season starts across the US; how the dates are worked out.