Mosquito season in Mercer County, NJ: when it starts and ends
Mosquito months in Mercer County
In a normal year mosquito season in Mercer County, NJ starts around April 10 and ends around October 30, about 29 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Mercer County, and when
- Start tipping out standing water weekly by March 27.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 30.
- 9 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.
Mercer County against the rest of NJ
Mercer County has the 12th longest season of 21 NJ counties, at 204 days against 217 in Cape May County and 184 in Sussex County. Its mean temperature is 53.4°F.
- Middlesex County: April 10 to November 1 (205 days, 20 WNV)
- Monmouth County: April 11 to November 2 (205 days, 25 WNV)
- Essex County: April 11 to October 28 (199 days, 10 WNV)
- Ocean County: April 14 to October 29 (198 days, 9 WNV)
West Nile in Mercer County
From 1999 to 2025, CDC ArboNET counted 23 human West Nile cases in Mercer County (16 neuroinvasive) across 12 years. The worst was 2002 with 4; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.