Mosquito season in Jefferson County, KY: when it starts and ends
Mosquito months in Jefferson County
In a normal year mosquito season in Jefferson County, KY starts around March 22 and ends around November 9, about 33 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 8.
- Book any yard treatment for late March, ahead of the July peak.
- Repellent can go away after November 9.
- 35 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to September, and check KY spray notices.
Jefferson County against the rest of KY
Jefferson County has the 6th longest season of 120 KY counties, at 232 days against 249 in Lyon County and 180 in Shelby County. Its mean temperature is 58.1°F.
- Christian County: March 22 to November 10 (233 days, 0 WNV)
- Ballard County: March 22 to November 9 (232 days, 0 WNV)
- Fulton County: March 23 to November 9 (231 days, 0 WNV)
- Calloway County: March 24 to November 10 (231 days, 0 WNV)
West Nile in Jefferson County
From 1999 to 2025, CDC ArboNET counted 81 human West Nile cases in Jefferson County (65 neuroinvasive) across 19 years. The worst was 2002 with 28; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.