Lyme disease is most common in the northeastern United States, the upper Midwest, and parts of northern Europe. In 2023, over 89,000 cases were reported to the CDC, but the actual number of people diagnosed and treated each year is estimated at roughly 476,000. The disease clusters tightly in specific regions where the right ticks, hosts, and habitat overlap.
The Highest-Risk States in the U.S.
Lyme disease is not spread evenly across the country. A handful of states account for the vast majority of cases, and the concentration is striking. In 2022, Rhode Island had the highest incidence rate at 212 cases per 100,000 people, followed closely by Vermont (204) and Maine (195). West Virginia came in fourth at 138 per 100,000.
The next tier includes Wisconsin (88), New York (83), New Hampshire (79), Massachusetts (72), Pennsylvania (65), New Jersey (64), and Connecticut (56). Minnesota rounds out the major hotspots at 47 per 100,000. Maryland, Delaware, and Virginia also see significant numbers, though at lower rates. If you live in the Northeast or upper Midwest, your risk is meaningfully higher than in most other parts of the country.
Why These Regions and Not Others
The blacklegged tick, which transmits Lyme disease, needs very specific conditions to survive. It requires temperatures above about 16°C (61°F) with high humidity for at least part of the year to complete its life cycle. Mild, wet winters boost survival, and spring rain helps ticks stay active longer. Warmer, drier climates cause them to lose water rapidly and die.
These ticks thrive in temperate forests with dense leaf litter, which insulates them from cold and maintains moisture at ground level. Snow cover actually helps them survive winter. The ideal habitat is essentially the deciduous and mixed forests stretching from the mid-Atlantic through New England and into the Great Lakes region. Habitat suitability drops to near zero where mean annual temperatures fall below roughly -10°C or rise above 25°C.
The blacklegged tick has been recorded in 37 states east of the Great Plains and is considered established in over 840 counties. A separate species, the western blacklegged tick, lives in six western states, primarily along the Pacific Coast. No single state has both species, and five Rocky Mountain states (Colorado, Idaho, Montana, New Mexico, and Wyoming) have no established populations of either.
Lyme Disease on the West Coast
Lyme disease does occur on the West Coast, but at far lower rates than in the Northeast. In Oregon, the western blacklegged tick is found from the western slope of the Cascade mountain range to the Pacific Ocean, with the highest disease rates in the southwestern portion of the state. A small area near the mouth of the Deschutes River in north-central Oregon is another pocket of risk. After adjusting for people who were likely bitten elsewhere, the case rate in southwestern Oregon is nearly five times higher than in the Portland area.
California, Oregon, and Washington hold the majority of western blacklegged tick populations. But even in these states, the overall risk remains low compared to endemic areas in the East. If you live on the West Coast and haven’t traveled to the Northeast or upper Midwest, a Lyme diagnosis is uncommon outside of those specific local hotspots.
Lyme Disease in Europe
Europe has its own significant Lyme disease burden, transmitted by a related tick species. The highest national incidence rates, exceeding 100 cases per 100,000 people per year, are found in Estonia, Lithuania, Slovenia, and Switzerland. The Netherlands reports some of the highest rates on the continent, with eastern provinces like Drenthe and Overijssel reaching 357 and 276 cases per 100,000 respectively.
In Finland, the Åland Islands (Ahvenanmaa) are hyperendemic, with an extraordinary rate of nearly 2,474 cases per 100,000 residents. Poland has Lyme disease in all regions, with the highest incidence in the eastern and northeastern parts of the country. In France, the highest-risk areas are in the Limousin region and the northeast. Germany’s eastern states also carry substantial risk. The disease has been reported in nearly every European country since the first case description in 1908.
The Range Is Expanding
Lyme disease territory is growing. In the United States, the number of counties with established tick populations has increased throughout almost all states east of the Mississippi and across much of the Midwest, reaching roughly to the 95th meridian. The expansion is driven largely by warmer winters that allow ticks to survive in places that were previously too cold.
Canada is seeing some of the most dramatic change. In Ontario, the blacklegged tick’s range is advancing at approximately 46 kilometers per year. In Quebec, the number of ticks collected more than quadrupled between 2008 and 2014, and the geographic range expanded simultaneously. Southern Manitoba and parts of the Maritime provinces are also seeing new tick populations establish. Areas that were essentially Lyme-free a decade ago now carry real risk.
When the Risk Is Highest
In the eastern United States, you can be bitten by an infected tick from spring through fall. The most dangerous window is April through July, when nymphal ticks (the immature stage, roughly the size of a poppy seed) are actively searching for hosts. These tiny nymphs cause the majority of human infections because they’re so small they often go unnoticed. Adult ticks are most active in early spring and again in fall, but their larger size makes them easier to spot and remove before they transmit the bacteria.
Urban Green Spaces Carry Risk Too
You don’t have to be deep in the woods to encounter Lyme-carrying ticks. Research across urban green spaces and rural woodlands in the UK found that nymphal ticks were present in 73% of urban parks and green spaces surveyed. Rural woodlands had higher overall rates (98% of sites) and roughly 3.6 times the tick density, but urban exposure is far from negligible.
In cities, tick density correlates with tree cover within a park, how well the green space connects to larger wooded areas, and how much built-up development surrounds it. Parks bordered by newer construction tend to have fewer ticks. In rural settings, the age of the woodland is the strongest predictor: older forests harbor more ticks. The practical takeaway is that tick checks after spending time in any wooded or leafy area are worthwhile, even in a suburban park in an endemic region.