Mosquito season in Cass County, MI: when it starts and ends
Mosquito months in Cass County
In a normal year mosquito season in Cass County, MI starts around April 24 and ends around October 20, about 26 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 10.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 20.
- 2 West Nile cases since 2016 (last 2021): you should use repellent at dusk July to August, more so if over 60.
Cass County against the rest of MI
Cass County has the 13th longest season of 83 MI counties, at 179 days against 189 in Allegan County and 124 in Iron County. Its mean temperature is 49.5°F.
- Ingham County: April 22 to October 18 (179 days, 12 WNV)
- St. Joseph County: April 22 to October 18 (179 days, 3 WNV)
- Branch County: April 23 to October 16 (176 days, 0 WNV)
- Oakland County: April 24 to October 17 (176 days, 62 WNV)
West Nile in Cass County
From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Cass County (5 neuroinvasive) across 3 years. The worst was 2002 with 4; the latest was 2021.
See how the dates are worked out, and when mosquitoes go away for the winter.