Mosquito season in Sioux County, IA: when it starts and ends
Mosquito months in Sioux County
In a normal year mosquito season in Sioux County, IA starts around April 21 and ends around October 14, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Sioux 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 14.
- 32 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check IA spray notices.
Sioux County against the rest of IA
Sioux County has the 60th longest season of 99 IA counties, at 176 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 47.8°F.
- Winneshiek County: April 22 to October 16 (177 days, 0 WNV)
- Wright County: April 22 to October 16 (177 days, 1 WNV)
- Buena Vista County: April 22 to October 15 (176 days, 2 WNV)
- Butler County: April 22 to October 15 (176 days, 1 WNV)
West Nile in Sioux County
From 1999 to 2025, CDC ArboNET counted 54 human West Nile cases in Sioux County (31 neuroinvasive) across 14 years. The worst was 2003 with 14; the latest was 2025.
See how the dates are worked out, and reading the West Nile counts.