Mosquito season in Tazewell County, IL: when it starts and ends

Mosquito months in Tazewell County

In a normal year mosquito season in Tazewell County, IL starts around April 8 and ends around October 26, about 29 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Tazewell County, and when

• Start tipping out standing water weekly by March 25.
• Book any yard treatment for early April, ahead of the July peak.
• Repellent can go away after October 26.
• 7 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.

Tazewell County against the rest of IL

Tazewell County has the 59th longest season of 102 IL counties, at 201 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 52.3°F.

• Marshall County: April 8 to October 26 (201 days, 1 WNV)
• Mason County: April 8 to October 26 (201 days, 0 WNV)
• Menard County: April 9 to October 26 (201 days, 0 WNV)
• Logan County: April 8 to October 25 (200 days, 0 WNV)

West Nile in Tazewell County

From 1999 to 2025, CDC ArboNET counted 13 human West Nile cases in Tazewell County (12 neuroinvasive) across 11 years. The worst was 2024 with 2; the latest was 2025.

See how the dates are worked out, and reading the West Nile counts.