Mosquito season in Corson County, SD: when it starts and ends

Mosquito months in Corson County

In a normal year mosquito season in Corson County, SD starts around April 30 and ends around October 7, about 23 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 Corson County, and when

• Start tipping out standing water weekly by April 16.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 7.
• 3 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.

Corson County against the rest of SD

Corson County has the 36th longest season of 66 SD counties, at 160 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 44.7°F.

• Bennett County: May 2 to October 10 (161 days, 1 WNV)
• Hyde County: May 2 to October 10 (161 days, 1 WNV)
• Dewey County: April 30 to October 7 (160 days, 11 WNV)
• Hanson County: April 30 to October 7 (160 days, 5 WNV)

West Nile in Corson County

From 1999 to 2025, CDC ArboNET counted 17 human West Nile cases in Corson County (5 neuroinvasive) across 10 years. The worst was 2003 with 7; the latest was 2025.

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