Mosquito season in Mason County, IL: when it starts and ends
Mosquito months in Mason County
In a normal year mosquito season in Mason 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 Mason 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.
- No West Nile cases since 2016, so bites in Mason County are a nuisance; check window screens.
Mason County against the rest of IL
Mason County has the 58th 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.
- Hancock County: April 8 to October 27 (201 days, 0 WNV)
- Marshall County: April 8 to October 26 (201 days, 1 WNV)
- Tazewell County: April 8 to October 26 (201 days, 7 WNV)
- Menard County: April 9 to October 26 (201 days, 0 WNV)
West Nile in Mason County
From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Mason County (1 neuroinvasive) across 3 years. The worst was 2015 with 2; the latest was 2015.
More: how the dates are worked out · when the season starts across the US.