Mosquito season in Shelby County, IL: when it starts and ends
Mosquito months in Shelby County
In a normal year mosquito season in Shelby County, IL starts around April 5 and ends around October 29, about 30 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Shelby County, and when
- Start tipping out standing water weekly by March 22.
- 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 Shelby County are a nuisance; check window screens.
Shelby County against the rest of IL
Shelby County has the 41st longest season of 102 IL counties, at 207 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 53.6°F.
- Macoupin County: April 4 to October 29 (207 days, 3 WNV)
- Christian County: April 5 to October 29 (207 days, 0 WNV)
- Jersey County: April 5 to October 28 (206 days, 1 WNV)
- Calhoun County: April 6 to October 29 (206 days, 0 WNV)
West Nile in Shelby County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Shelby County (0 neuroinvasive) across 1 year. The worst was 2002 with 3; the latest was 2002.
Background: when mosquitoes go away for the winter; how the dates are worked out.