Mosquito season in Cass County, MN: when it starts and ends
Mosquito months in Cass County
In a normal year mosquito season in Cass County, MN starts around May 3 and ends around October 4, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Cass County, and when
- Start tipping out standing water weekly by April 19.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 4.
- 4 West Nile cases since 2016 (last 2025): you should use repellent at dusk July, more so if over 60.
Cass County against the rest of MN
Cass County has the 60th longest season of 87 MN counties, at 153 days against 176 in Winona County and 118 in Cook County. Its mean temperature is 41.7°F.
- Crow Wing County: May 3 to October 4 (154 days, 2 WNV)
- Fillmore County: May 4 to October 5 (154 days, 2 WNV)
- Kanabec County: May 4 to October 4 (153 days, 0 WNV)
- Mille Lacs County: May 4 to October 4 (153 days, 3 WNV)
West Nile in Cass County
From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Cass County (3 neuroinvasive) across 5 years. The worst was 2024 with 2; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.