Mosquito season in Douglas County, IL: when it starts and ends
Mosquito months in Douglas County
In a normal year mosquito season in Douglas County, IL starts around April 8 and ends around October 27, about 29 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Douglas County, and when
- Start tipping out standing water weekly by March 25.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 27.
- 1 West Nile case since 2016 (last 2017): you should use repellent at dusk June to August, more so if over 60.
Douglas County against the rest of IL
Douglas County has the 55th longest season of 102 IL counties, at 201 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 52.5°F.
- Morgan County: April 8 to October 27 (202 days, 1 WNV)
- Cass County: April 8 to October 27 (201 days, 0 WNV)
- Hancock County: April 8 to October 27 (201 days, 0 WNV)
- Marshall County: April 8 to October 26 (201 days, 1 WNV)
West Nile in Douglas County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Douglas County (0 neuroinvasive) across 1 year. The worst was 2017 with 1; the latest was 2017.
Background: when mosquitoes go away for the winter; how the dates are worked out.