Mosquito season in Franklin County, IL: when it starts and ends
Mosquito months in Franklin County
In a normal year mosquito season in Franklin County, IL starts around March 27 and ends around November 4, about 32 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Franklin County, and when
- Start tipping out standing water weekly by March 13.
- Book any yard treatment for late March, ahead of the July peak.
- Repellent can go away after November 4.
- 8 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.
Franklin County against the rest of IL
Franklin County has the 10th longest season of 102 IL counties, at 222 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 56.2°F.
- Massac County: March 27 to November 5 (223 days, 4 WNV)
- Wayne County: March 27 to November 5 (223 days, 1 WNV)
- Wabash County: March 28 to November 4 (221 days, 1 WNV)
- Perry County: March 28 to November 2 (219 days, 0 WNV)
West Nile in Franklin County
From 1999 to 2025, CDC ArboNET counted 14 human West Nile cases in Franklin County (11 neuroinvasive) across 11 years. The worst was 2025 with 2; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.