Mosquito season in Johnson County, IL: when it starts and ends
Mosquito months in Johnson County
In a normal year mosquito season in Johnson County, IL starts around April 2 and ends around October 31, about 30 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Johnson County, and when
- Start tipping out standing water weekly by March 19.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 31.
- No West Nile cases since 2016, so bites in Johnson County are a nuisance; check window screens.
Johnson County against the rest of IL
Johnson County has the 27th longest season of 102 IL counties, at 212 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 57.6°F.
- Hamilton County: April 1 to October 30 (212 days, 0 WNV)
- Jefferson County: April 2 to October 31 (212 days, 1 WNV)
- Pope County: April 2 to October 31 (212 days, 0 WNV)
- Coles County: April 3 to October 31 (211 days, 4 WNV)
West Nile in Johnson County
CDC ArboNET lists no human West Nile cases for Johnson County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 8 of those years.
Background: when mosquitoes go away for the winter; how the dates are worked out.