These 10 Counties See The biggest Surge in Lyme Disease

By Evan Comen  •  May 11, 2026
A red tick clings to a green plant stem.
Photo by Erik Karits on Unsplash

A warming climate means more favorable conditions for disease-carrying vectors such as mosquitoes, ticks, and fleas. Deer ticks especially thrive in temperatures above 45°F, which are becoming more common as winters grow shorter and milder. As the range of habitat for ticks increases, so does the risk of Lyme disease.

Reported cases of Lyme disease have surged across the Northeast in the last 15 years, and spread into regions where the illness was once rare. In Maine, the incidence rate jumped nearly tenfold, increasing by more than 100 new cases for every 100,000 residents. Vermont and West Virginia have experienced similar increases, while states farther west — including Wisconsin, Iowa, and Michigan — are also seeing rapid growth. A closer look at the data reveals fast-warming counties where Lyme disease is accelerating.

To determine the counties where climate change is contributing to an increase in Lyme disease, Climate Crisis 247 reviewed data on Lyme disease incidence from the Centers for Disease Control and Prevention. Counties were ranked based on the 15-year change in the incidence rate of Lyme disease per 100,000 residents from 2004-2006 to 2019-2021. Supplemental data on average temperature are from the NOAA.

10. Venango County, PA

  • Increase in Lyme disease incidence in last 15 years: +181.7 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 0.6 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 182.4 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 68.6°F (+1.6° above normal)
  • County seat: Franklin

9. Wayne County, PA

  • Increase in Lyme disease incidence in last 15 years: +183.4 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 13.0 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 196.4 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 67.6°F (+1.9° above normal)
  • County seat: Honesdale

8. Marquette County, WI

  • Increase in Lyme disease incidence in last 15 years: +186.4 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 52.0 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 238.4 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 69.9°F (+1.5° above normal)
  • County seat: Montello

7. Marinette County, WI

  • Increase in Lyme disease incidence in last 15 years: +191.0 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 10.7 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 201.8 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 66.4°F (+1.6° above normal)
  • County seat: Marinette

6. Florence County, WI

  • Increase in Lyme disease incidence in last 15 years: +193.3 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 7.7 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 201.0 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 64.7°F (+2.2° above normal)
  • County seat: Florence
white wooden house near green trees during daytime
Photo by Yoav Hornung on Unsplash

5. Lincoln County, ME

  • Increase in Lyme disease incidence in last 15 years: +213.1 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 40.7 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 253.8 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 66.8°F (+2.6° above normal)
  • County seat: Wiscasset

4. Dickinson County, MI

  • Increase in Lyme disease incidence in last 15 years: +224.6 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 1.3 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 226.0 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 65.3°F (+2.4° above normal)
  • County seat: Iron Mountain

3. Waldo County, ME

  • Increase in Lyme disease incidence in last 15 years: +282.0 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 9.2 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 291.2 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 66.5°F (+2.4° above normal)
  • County seat: Belfast

2. Hancock County, ME

  • Increase in Lyme disease incidence in last 15 years: +290.6 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 10.3 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 300.9 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 66.5°F (+2.5° above normal)
  • County seat: Ellsworth

1. Knox County, ME

  • Increase in Lyme disease incidence in last 15 years: +373.4 cases per 100,000 residents
  • Lyme disease incidence rate, 2004-2006: 37.7 cases per 100,000 residents
  • Lyme disease incidence rate, 2019-2021: 411.1 cases per 100,000 residents
  • Average summer temperature, 2021-2023: 65.9°F (+2.5° above normal)
  • County seat: Rockland


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