Mosquito season in Carroll County, IL: when it starts and ends
Mosquito months in Carroll County
In a normal year mosquito season in Carroll County, IL starts around April 23 and ends around October 16, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Carroll County, and when
- Start tipping out standing water weekly by April 9.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 16.
- 2 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Carroll County against the rest of IL
Carroll County has the 101st longest season of 102 IL counties, at 176 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 48.8°F.
- Stephenson County: April 22 to October 16 (177 days, 3 WNV)
- Winnebago County: April 23 to October 16 (177 days, 11 WNV)
- Boone County: April 24 to October 15 (174 days, 2 WNV)
West Nile in Carroll County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Carroll County (3 neuroinvasive) across 3 years. The worst was 2025 with 1; the latest was 2025.
Background: when mosquitoes go away for the winter; how the dates are worked out.