Mosquito season in Brown County, SD: when it starts and ends
Mosquito months in Brown County
In a normal year mosquito season in Brown 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 Brown 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.
- 71 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to July, and check SD spray notices.
Brown County against the rest of SD
Brown County has the 44th longest season of 66 SD counties, at 159 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 43.3°F.
- Potter County: May 1 to October 7 (160 days, 9 WNV)
- Pennington County: May 2 to October 9 (160 days, 32 WNV)
- Sanborn County: April 30 to October 6 (159 days, 6 WNV)
- Moody County: May 1 to October 7 (159 days, 3 WNV)
West Nile in Brown County
From 1999 to 2025, CDC ArboNET counted 346 human West Nile cases in Brown County (60 neuroinvasive) across 21 years. The worst was 2003 with 90; the latest was 2025.
See how the dates are worked out, and reading the West Nile counts.