Mosquito season in Jefferson County, IA: when it starts and ends
Mosquito months in Jefferson County
In a normal year mosquito season in Jefferson County, IA starts around April 15 and ends around October 20, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Jefferson County, and when
- Start tipping out standing water weekly by April 1.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 20.
- No West Nile cases since 2016, so bites in Jefferson County are a nuisance; check window screens.
Jefferson County against the rest of IA
Jefferson County has the 19th longest season of 99 IA counties, at 188 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 49.7°F.
- Monroe County: April 15 to October 21 (189 days, 1 WNV)
- Taylor County: April 15 to October 21 (189 days, 0 WNV)
- Louisa County: April 15 to October 20 (188 days, 0 WNV)
- Pottawattamie County: April 16 to October 21 (188 days, 18 WNV)
West Nile in Jefferson County
CDC ArboNET lists no human West Nile cases for Jefferson County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 6 of those years.
See how the dates are worked out, and when mosquitoes go away for the winter.