Mosquito season in Randolph County, IL: when it starts and ends
Mosquito months in Randolph County
In a normal year mosquito season in Randolph County, IL starts around April 1 and ends around November 1, about 31 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Randolph County, and when
- Start tipping out standing water weekly by March 18.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after November 1.
- 1 West Nile case since 2016 (last 2022): you should use repellent at dusk June to August, more so if over 60.
Randolph County against the rest of IL
Randolph County has the 20th longest season of 102 IL counties, at 214 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 55.5°F.
- Washington County: March 31 to November 2 (216 days, 0 WNV)
- Bond County: March 31 to November 2 (215 days, 1 WNV)
- Lawrence County: April 2 to November 1 (214 days, 0 WNV)
- Montgomery County: April 2 to November 2 (214 days, 0 WNV)
West Nile in Randolph County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Randolph County (1 neuroinvasive) across 1 year. The worst was 2022 with 1; the latest was 2022.
See how the dates are worked out, and when the season starts across the US.