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

Mosquito months in Yankton County

In a normal year mosquito season in Yankton County, SD starts around April 21 and ends around October 16, 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 Yankton County, and when

• Start tipping out standing water weekly by April 7.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 16.
• 20 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check SD spray notices.

Yankton County against the rest of SD

Yankton County has the 1st longest season of 66 SD counties, at 179 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 48.5°F.

• Tripp County: April 22 to October 18 (179 days, 4 WNV)
• Douglas County: April 21 to October 16 (178 days, 11 WNV)

West Nile in Yankton County

From 1999 to 2025, CDC ArboNET counted 46 human West Nile cases in Yankton County (14 neuroinvasive) across 13 years. The worst was 2003 with 11; the latest was 2025.

See how the dates are worked out, and reading the West Nile counts.