Mosquito season in Sanborn County, SD: when it starts and ends
Mosquito months in Sanborn County
In a normal year mosquito season in Sanborn County, SD starts around April 30 and ends around October 6, about 23 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Sanborn 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 6.
- 6 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Sanborn County against the rest of SD
Sanborn County has the 45th longest season of 66 SD counties, at 159 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 45.7°F.
- Pennington County: May 2 to October 9 (160 days, 32 WNV)
- Brown County: April 30 to October 6 (159 days, 71 WNV)
- Moody County: May 1 to October 7 (159 days, 3 WNV)
- Walworth County: May 1 to October 7 (159 days, 17 WNV)
West Nile in Sanborn County
From 1999 to 2025, CDC ArboNET counted 32 human West Nile cases in Sanborn County (5 neuroinvasive) across 13 years. The worst was 2003 with 12; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.