Mosquito season in Jefferson County, IN: when it starts and ends
Mosquito months in Jefferson County
In a normal year mosquito season in Jefferson County, IN starts around March 31 and ends around November 4, about 31 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 March 17.
- Book any yard treatment for late March, ahead of the July peak.
- Repellent can go away after November 4.
- 2 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.
Jefferson County against the rest of IN
Jefferson County has the 9th longest season of 92 IN counties, at 218 days against 231 in Floyd County and 177 in Steuben County. Its mean temperature is 55.6°F.
- Warrick County: March 30 to November 3 (218 days, 1 WNV)
- Dubois County: March 31 to November 4 (218 days, 1 WNV)
- Perry County: March 31 to November 4 (218 days, 1 WNV)
- Greene County: March 31 to November 3 (217 days, 1 WNV)
West Nile in Jefferson County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Jefferson County (2 neuroinvasive) across 2 years. The worst was 2025 with 2; the latest was 2025.
Background: when the season starts across the US; how the dates are worked out.