Mosquito season in Sibley County, MN: when it starts and ends

Mosquito months in Sibley County

In a normal year mosquito season in Sibley County, MN starts around April 26 and ends around October 11, about 24 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 Sibley County, and when

• Start tipping out standing water weekly by April 12.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 11.
• 6 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.

Sibley County against the rest of MN

Sibley County has the 15th longest season of 87 MN counties, at 167 days against 176 in Winona County and 118 in Cook County. Its mean temperature is 44.9°F.

• Freeborn County: April 26 to October 11 (167 days, 1 WNV)
• Nicollet County: April 26 to October 11 (167 days, 2 WNV)
• Waseca County: April 26 to October 10 (167 days, 2 WNV)
• Morrison County: April 27 to October 10 (167 days, 2 WNV)

West Nile in Sibley County

From 1999 to 2025, CDC ArboNET counted 8 human West Nile cases in Sibley County (3 neuroinvasive) across 6 years. The worst was 2025 with 3; the latest was 2025.

More: how the dates are worked out · reading the West Nile counts.