Presence of black-legged ticks across the U.S.

There are two species of ticks that can carry Lyme disease, black-legged ticks, commonly known as deer ticks, and western black-legged ticks. They are mostly present on the West Coast and the eastern half of the United States.

"No record" counties do not guarantee tick absence. These counties could have shortages in sampling efforts, tick collection, reporting or publishing sampling efforts.

A tick population is considered "established" by the CDC if six or more ticks of the same life stage, or more than one life stage of a tick species is collected in a county within a 12-month period. Tick species are "reported" when fewer than six ticks of the same life stage have been collected over a 12-month period.

Data for contiguous United States as of Dec. 31, 2024.
Chart: Annetta StogniewSource: CDCCreated with Datawrapper