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

Mosquito months in Fall River County

In a normal year mosquito season in Fall River County, SD starts around May 5 and ends around October 7, about 22 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 Fall River County, and when

• Start tipping out standing water weekly by April 21.
• Book any yard treatment for early May, ahead of the July peak.
• Repellent can go away after October 7.
• 1 West Nile case since 2016 (last 2023): you should use repellent at dusk July to August, more so if over 60.

Fall River County against the rest of SD

Fall River County has the 60th longest season of 66 SD counties, at 155 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 47.9°F.

• Hamlin County: May 3 to October 5 (155 days, 12 WNV)
• Lyman County: May 3 to October 5 (155 days, 4 WNV)
• McPherson County: May 4 to October 3 (152 days, 4 WNV)
• Harding County: May 5 to October 5 (152 days, 0 WNV)

West Nile in Fall River County

From 1999 to 2025, CDC ArboNET counted 32 human West Nile cases in Fall River County (11 neuroinvasive) across 8 years. The worst was 2003 with 25; the latest was 2023.

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