Mosquito season in Clark County, IL: when it starts and ends
Mosquito months in Clark County
In a normal year mosquito season in Clark County, IL starts around April 5 and ends around October 30, about 30 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Clark 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 30.
- No West Nile cases since 2016, so bites in Clark County are a nuisance; check window screens.
Clark County against the rest of IL
Clark County has the 38th longest season of 102 IL counties, at 208 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 53.7°F.
- White County: April 3 to October 28 (208 days, 0 WNV)
- Pike County: April 4 to October 30 (208 days, 0 WNV)
- Macoupin County: April 4 to October 29 (207 days, 3 WNV)
- Christian County: April 5 to October 29 (207 days, 0 WNV)
West Nile in Clark County
From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Clark County (1 neuroinvasive) across 1 year. The worst was 2002 with 2; the latest was 2002.
More: how the dates are worked out · when mosquitoes go away for the winter.