Mosquito season in Jefferson County, PA: when it starts and ends
Mosquito months in Jefferson County
In a normal year mosquito season in Jefferson County, PA starts around April 25 and ends around October 14, about 25 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 11.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 14.
- No West Nile cases since 2016, so bites in Jefferson County are a nuisance; check window screens.
Jefferson County against the rest of PA
Jefferson County has the 48th longest season of 67 PA counties, at 173 days against 222 in Philadelphia County and 154 in Clinton County. Its mean temperature is 47.4°F.
- Butler County: April 26 to October 17 (174 days, 1 WNV)
- Monroe County: April 24 to October 14 (173 days, 3 WNV)
- Carbon County: April 25 to October 14 (172 days, 1 WNV)
- Cameron County: April 27 to October 14 (170 days, 0 WNV)
West Nile in Jefferson County
From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Jefferson County (3 neuroinvasive) across 2 years. The worst was 2003 with 3; the latest was 2003.
Background: when the season starts across the US; how the dates are worked out.