Mosquito season in St. Joseph County, MI: when it starts and ends

Mosquito months in St. Joseph County

In a normal year mosquito season in St. Joseph County, MI starts around April 22 and ends around October 18, about 26 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in St. Joseph County, and when

• Start tipping out standing water weekly by April 8.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 18.
• 3 West Nile cases since 2016 (last 2018): you should use repellent at dusk July to July, more so if over 60.

St. Joseph County against the rest of MI

St. Joseph County has the 12th longest season of 83 MI counties, at 179 days against 189 in Allegan County and 124 in Iron County. Its mean temperature is 48.7°F.

• Clinton County: April 23 to October 20 (180 days, 4 WNV)
• Ingham County: April 22 to October 18 (179 days, 12 WNV)
• Cass County: April 24 to October 20 (179 days, 2 WNV)
• Branch County: April 23 to October 16 (176 days, 0 WNV)

West Nile in St. Joseph County

From 1999 to 2025, CDC ArboNET counted 7 human West Nile cases in St. Joseph County (3 neuroinvasive) across 3 years. The worst was 2018 with 3; the latest was 2018.

See how the dates are worked out, and when the season starts across the US.