Mosquito season in Marshall County, IL: when it starts and ends
Mosquito months in Marshall County
In a normal year mosquito season in Marshall County, IL starts around April 8 and ends around October 26, about 29 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Marshall 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 26.
- 1 West Nile case since 2016 (last 2023): you should use repellent at dusk June to August, more so if over 60.
Marshall County against the rest of IL
Marshall County has the 57th longest season of 102 IL counties, at 201 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 52.3°F.
- Douglas County: April 8 to October 27 (201 days, 1 WNV)
- Hancock County: April 8 to October 27 (201 days, 0 WNV)
- Mason County: April 8 to October 26 (201 days, 0 WNV)
- Tazewell County: April 8 to October 26 (201 days, 7 WNV)
West Nile in Marshall County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Marshall County (1 neuroinvasive) across 3 years. The worst was 2023 with 1; the latest was 2023.
More: how the dates are worked out · when the season starts across the US.