Mosquito season in Morris County, NJ: when it starts and ends
Mosquito months in Morris County
In a normal year mosquito season in Morris County, NJ starts around April 18 and ends around October 22, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Morris County, and when
- Start tipping out standing water weekly by April 4.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 22.
- 8 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Morris County against the rest of NJ
Morris County has the 19th longest season of 21 NJ counties, at 188 days against 217 in Cape May County and 184 in Sussex County. Its mean temperature is 50.6°F.
- Somerset County: April 15 to October 26 (194 days, 9 WNV)
- Passaic County: April 17 to October 26 (192 days, 7 WNV)
- Warren County: April 18 to October 21 (186 days, 7 WNV)
- Sussex County: April 19 to October 20 (184 days, 2 WNV)
West Nile in Morris County
From 1999 to 2025, CDC ArboNET counted 13 human West Nile cases in Morris County (9 neuroinvasive) across 9 years. The worst was 2018 with 4; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.