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

Mosquito months in Effingham County

In a normal year mosquito season in Effingham County, IL starts around April 3 and ends around October 31, about 30 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 Effingham County, and when

• Start tipping out standing water weekly by March 20.
• Book any yard treatment for early April, ahead of the July peak.
• Repellent can go away after October 31.
• 1 West Nile case since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.

Effingham County against the rest of IL

Effingham County has the 31st longest season of 102 IL counties, at 211 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 54.4°F.

• Coles County: April 3 to October 31 (211 days, 4 WNV)
• Cumberland County: April 3 to October 31 (211 days, 0 WNV)
• Jasper County: April 3 to October 31 (211 days, 0 WNV)
• Fayette County: April 2 to October 30 (210 days, 0 WNV)

West Nile in Effingham County

From 1999 to 2025, CDC ArboNET counted 10 human West Nile cases in Effingham County (4 neuroinvasive) across 3 years. The worst was 2002 with 7; the latest was 2025.

Background: when mosquitoes go away for the winter; how the dates are worked out.