Climate Change Is Expanding Tick Habitats, Accelerating Lyme Disease Spread in These Counties

Detailed close-up of a deer tick crawling on a green leaf, emphasizing its role as a disease vector.

https://climate-crisis-247-bucket.nyc3.digitaloceanspaces.com/wp-content/uploads/2025/09/07202812/5083105-150x150.jpeg

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.

25. Adams County, WI

Increase in Lyme disease incidence in last 15 years: +127.0 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 47.8 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 174.8 cases per 100,000 residents
Average summer temperature, 2021-2023: 69.2°F (+1.5° above normal)
County seat: Friendship

24. Barbour County, WV

Increase in Lyme disease incidence in last 15 years: +133.0 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 2.0 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 135.0 cases per 100,000 residents
Average summer temperature, 2021-2023: 70.6°F (+1.4° above normal)
County seat: Philippi

23. Kennebec County, ME

Increase in Lyme disease incidence in last 15 years: +143.5 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 11.7 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 155.3 cases per 100,000 residents
Average summer temperature, 2021-2023: 67.4°F (+2.3° above normal)
County seat: Augusta

22. Monroe County, WV

Increase in Lyme disease incidence in last 15 years: +144.9 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 2.5 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 147.4 cases per 100,000 residents
Average summer temperature, 2021-2023: 70.3°F (+0.8° above normal)
County seat: Union

21. Grand Isle County, VT

Increase in Lyme disease incidence in last 15 years: +146.1 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 4.7 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 150.8 cases per 100,000 residents
Average summer temperature, 2021-2023: 69.0°F (+1.7° above normal)
County seat: North Hero

20. Forest County, PA

Increase in Lyme disease incidence in last 15 years: +148.4 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 9.3 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 157.6 cases per 100,000 residents
Average summer temperature, 2021-2023: 67.7°F (+1.6° above normal)
County seat: Tionesta

19. Cortland County, NY

Increase in Lyme disease incidence in last 15 years: +150.5 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 1.4 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 151.9 cases per 100,000 residents
Average summer temperature, 2021-2023: 66.4°F (+1.0° above normal)
County seat: Cortland

18. Schuyler County, NY

Increase in Lyme disease incidence in last 15 years: +156.9 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 1.9 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 158.8 cases per 100,000 residents
Average summer temperature, 2021-2023: 67.8°F (+1.4° above normal)
County seat: Watkins Glen

17. Wyoming County, PA

Increase in Lyme disease incidence in last 15 years: +162.5 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 8.6 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 171.1 cases per 100,000 residents
Average summer temperature, 2021-2023: 68.9°F (+2.1° above normal)
County seat: Tunkhannock

16. Door County, WI

Increase in Lyme disease incidence in last 15 years: +166.5 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 6.0 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 172.6 cases per 100,000 residents
Average summer temperature, 2021-2023: 66.2°F (+1.4° above normal)
County seat: Sturgeon Bay

15. Menominee County, WI

Increase in Lyme disease incidence in last 15 years: +167.9 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 14.6 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 182.5 cases per 100,000 residents
Average summer temperature, 2021-2023: 66.8°F (+1.8° above normal)
County seat: Keshena

14. Oconto County, WI

Increase in Lyme disease incidence in last 15 years: +177.8 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 1.8 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 179.6 cases per 100,000 residents
Average summer temperature, 2021-2023: 66.8°F (+1.4° above normal)
County seat: Oconto

13. Susquehanna County, PA

Increase in Lyme disease incidence in last 15 years: +179.8 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 6.6 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 186.4 cases per 100,000 residents
Average summer temperature, 2021-2023: 68.0°F (+1.8° above normal)
County seat: Montrose

12. Marshall County, WV

Increase in Lyme disease incidence in last 15 years: +180.2 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 1.1 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 181.2 cases per 100,000 residents
Average summer temperature, 2021-2023: 71.0°F (+0.5° above normal)
County seat: Moundsville

11. Clarion County, PA

Increase in Lyme disease incidence in last 15 years: +181.2 cases per 100,000 residents
Lyme disease incidence rate, 2004-2006: 6.0 cases per 100,000 residents
Lyme disease incidence rate, 2019-2021: 187.2 cases per 100,000 residents
Average summer temperature, 2021-2023: 68.6°F (+1.4° above normal)
County seat: Clarion

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

*Photo by Yevhen Kovalevskyi on Unsplash*

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

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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