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

Mosquito months in Coles County

In a normal year mosquito season in Coles 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 Coles 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.
• 4 West Nile cases since 2016 (last 2024): you should use repellent at dusk June to August, more so if over 60.

Coles County against the rest of IL

Coles County has the 29th longest season of 102 IL counties, at 211 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 54.2°F.

• Johnson County: April 2 to October 31 (212 days, 0 WNV)
• Pope County: April 2 to October 31 (212 days, 0 WNV)
• Cumberland County: April 3 to October 31 (211 days, 0 WNV)
• Effingham County: April 3 to October 31 (211 days, 1 WNV)

West Nile in Coles County

From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Coles County (4 neuroinvasive) across 5 years. The worst was 2023 with 2; the latest was 2024.

See how the dates are worked out, and reading the West Nile counts.