Stage 2 · Understanding the illness · surveillance data
Lyme, mapped
Reported cases by state and year, with the counting rules on the map.
Stage 2 · Understanding the illness · surveillance data
Lyme, mapped
Where reported Lyme disease lands, county by county and state by state, from CDC’s own surveillance data — with the counting rules drawn on the map, because a map without them is a rumor with a legend. Nothing here reads from any LymeHQ record.
What this map shows
Two maps. The first colours every county CDC counts by its reported cases, any year from 2001 to 2023, and lets you find your own county. From 2020 on, the years the Census population file covers, a county with 20 or more cases also gets a rate per 100,000 residents. The second shows each state, any year from 1992 to 2023, in powers of ten. Every count on both is in a table beside the picture — the colours orient, the numbers answer.
No count is not zero. A hatched county or state is the most misread thing on this page: it means no figure was published for that place and year, never that nobody had Lyme there.
Where it does not come from
Nothing here reads from any LymeHQ record. This map is built from public, external sources only, and every layer on it names its source, its date, and what it cannot say — on the map itself, where a screenshot keeps them.
That is checked rather than promised: a check walks this page’s imports in full and goes red if any of them can reach patient data — and it has to catch a planted leak in a committed fixture on the same run, so “the graph is clean” and “nobody looked” cannot produce the same green.
32 surveillance years · snapshot retrieved 2026-08-27
Lyme disease by county, 2023
CDC’s reported Lyme cases by county, 2023. Darker means more cases.
Cases reported in 2023
- 0
- 1–4
- 5–19
- 20–99
- 100–499
- 500 or more
- No count (never zero)
Showing reported cases by county for 2023.
What this map cannot say
- Reported counts depend on who was tested and reported, and are counted where people live, not where they were bitten. A low count does not mean there are no ticks.
- CDC: “After the implementation of a revised surveillance case definition in 2022, high-incidence jurisdictions report cases based on laboratory evidence alone, without the need for case investigation to obtain clinical information.” So years from 2022 on are not compared with earlier years here.
- A rate is LymeHQ's calculation, not CDC's: reported cases ÷ the Census estimate of residents on July 1 of the same year × 100,000. It is shown only where a county reported 20 or more cases that year, and only for the years the Census population file covers (from 2020). This build carries that file for 2020 to 2024, read 16 October 2026.
2023: 3,143 counties have a count in CDC’s county file and 10 have none. 13 of the areas with a count have no shape on this map (Chugach Census Area, Alaska; Connecticut’s planning regions; Falls Church city, Virginia; Lexington city, Virginia; Manassas Park city, Virginia); they are in the table. The county rows add up to 88,672 cases; CDC’s national total for 2023, from its state data set on data.cdc.gov (retrieved 2026-08-27), is 89,469, so 797 of them are on no county here.
- CDC, Lyme disease case counts by county (opens in a new tab), read 10 October 2026.
- CDC, MMWR 2024;73:118–123 (opens in a new tab), read 15 October 2026.
- U.S. Census Bureau, County Population Totals: 2020-2024 (Vintage 2024), resident population on July 1 (opens in a new tab), read 16 October 2026.
- County shapes: U.S. Census Bureau, Cartographic boundary files, counties, 1:10,000,000, 2017 edition (via the us-atlas package), read 15 October 2026. Alaska and Hawaii are moved and rescaled to fit.
Find a county
Your ZIP code and your location are matched to a county on this device. This page sends neither anywhere and saves neither, and nothing you choose here, the county included, goes into its address.
Looked up on this device.
Or use where you are
Your browser asks first. The point is matched to a county here.
The map as a table
Choose a state to list its counties, or every state.
The tick column (Ixodes scapularis, Ixodes pacificus) is added when CDC’s county tick tables are shown; why they are not yet is in each county’s panel.
By state, 1992 to 2023
Reported Lyme disease cases by state, 2023
2023 · CDC Lyme disease surveillance
89,469 cases reported nationally for 2023
Counting rules changed in 2008 and 2022, among other revisions — a jump across those years is partly surveillance artifact, not epidemiology. From 2022, high-incidence states report on laboratory evidence alone, so 2022 and later are not compared with earlier years on this page.
- 1–9
- 10–99
- 100–999
- 1,000–9,999
- 10,000+
- No count published — not zero risk
Not on the map: 54 withheld below state level by CDC (too few to show). Real cases, no state to draw them in.
Every jurisdiction with a published count for 2023 (44), as a list
| Jurisdiction | reported cases |
|---|---|
| New York | 22,173 |
| Pennsylvania | 16,671 |
| Massachusetts | 9,715 |
| New Jersey | 7,224 |
| Wisconsin | 6,283 |
| West Virginia | 3,242 |
| Connecticut | 3,239 |
| Maine | 2,942 |
| Minnesota | 2,938 |
| Rhode Island | 2,852 |
| Maryland | 2,470 |
| Virginia | 1,747 |
| New Hampshire | 1,573 |
| Vermont | 1,445 |
| Ohio | 1,307 |
| Michigan | 1,150 |
| Illinois | 372 |
| Delaware | 349 |
| Florida | 271 |
| Indiana | 257 |
| North Carolina | 228 |
| Iowa | 212 |
| Kentucky | 120 |
| California | 109 |
| District of Columbia | 108 |
| Oregon | 61 |
| South Carolina | 55 |
| Tennessee | 50 |
| Alabama | 34 |
| Colorado | 29 |
| Texas | 27 |
| Washington | 25 |
| Georgia | 17 |
| Utah | 16 |
| Missouri | 15 |
| Louisiana | 14 |
| Nevada | 14 |
| North Dakota | 12 |
| Arizona | 11 |
| Idaho | 11 |
| Kansas | 8 |
| New Mexico | 8 |
| Montana | 6 |
| South Dakota | 5 |
No published count for 2023 (not reported, or withheld below CDC’s display floor — not zero): Alaska, Arkansas, Hawaii, Mississippi, Nebraska, Oklahoma, Wyoming.
What this layer cannot say
- These are reported cases under the national surveillance definition, not infections — CDC-published claims analyses estimate roughly 476,000 people may be diagnosed with and treated for Lyme disease each year in the United States (Kugeler et al., Emerging Infectious Diseases, 2021; CDC, Lyme disease data and surveillance, read 25 September 2026), several times these totals. CDC notes this may be an overestimate, because billing codes do not always reflect a confirmed diagnosis — and it counts people diagnosed and treated, not people infected.
- 44 jurisdictions have a published count for 2023. A hatched state has no published state-level count — it did not report, or its count was below CDC's display floor and was withheld into the suppressed line. Either way, absence here is not evidence of absence there, and it is never zero risk.
- Counting rules in force: Case definition revised: high-incidence jurisdictions count laboratory evidence alone, and most cases are classified Probable. Jumps at this boundary are partly surveillance artifact, not epidemiology. Comparing years across a definition change compares the definitions too.
Reading the empty states
The hatched places are the most important thing on these maps, and the easiest to misread. A hatched state has no published state-level count for that year — and that absence is ambiguous by design: the state may not have reported to CDC at all, or it may have reported a count small enough that CDC withheld it rather than point at individual people. A hatched county has no count in CDC’s county file for that year: a blank in the file, or a place that was not a reporting unit then (Connecticut counted by planning region from 2023). What the hatching never means is zero.
Blacklegged ticks do not respect surveillance boundaries, and a state that left the published record did not stop having Lyme. Reading absence as safety is the one mistake this map is built to refuse — which is why an empty state is hatched and labelled rather than painted the palest green.
Ticks · a lookup about a place, never a meter about a person
By county: what CDC’s tick tables record
These are tables about ticks, not people. CDC marks a county established or reported for each tick by how many were collected there, and present for a germ found in at least one tick collected from vegetation. Where CDC has nothing, it says no records, and its page says: “Counties classified as "no records" should not be interpreted as the tick being absent. No records could be a result of a lack of sampling efforts, tick collections, or a lack of reporting or publishing the results of sampling efforts.” None of it is about you, your bite, or your odds.
Source: CDC, Tick Surveillance Data Sets (page updated May 14, 2026), read 15 October 2026. Finer than a county, by neighbourhood: Blocked upstream The data needs a sharing agreement we do not have.
Today:CDC’s tick maps (opens in a new tab)What else ticks carryTick identificationThe register, with a proof for every row
Reconciliation · one county, two counts
Why this page compares no LymeHQ count with CDC’s
- CDC · reported
- by county, on the map
- CDC’s county file counts reported cases where people live, 2001 to 2023. It is the county map above.
- LymeHQ · contributed
- not on this page
- No member figure appears on the open map, by design — and this page’s import graph is walked to prove one cannot.
- Overlap
- unknown
- No record linkage exists, by design, so nobody can say how many people are in both counts.
The two counts would disagree, and should. CDC counts what a provider reported to a health department under a case definition; LymeHQ would count people who chose to contribute a record that carries a diagnosis. Neither is the number of people with Lyme in a county, and neither can separate “fewer infections” from “fewer reports”.
How we would know we are wrong
If this snapshot is right, re-deriving it from the live source returns the same figures. A scheduled check re-pulls sampled years and state-years from data.cdc.gov and goes red when they stop matching — a red means CDC revised the data, and the snapshot is re-pulled rather than argued with.
The counting-rule changes of 2008 and 2022 are the two marked breaks; CDC lists other versions of the definition too (1995, 1996, 2008, 2011, 2017 and 2022). A jump across either is partly surveillance artifact, so anything that looks like a trend across one is suspect until the definition has been in force long enough to compare like with like.
What we publish, and how to check it →Where the numbers come from
The state map renders the same verified CDC snapshot as the case counts guide, pulled from data.cdc.gov and refused unless every year’s state figures plus CDC’s withheld and unknown residuals reconcile exactly to the national total. A scheduled check re-derives sampled years and state-years from the live source and goes red if they no longer match this snapshot — a red means CDC revised the data, and the snapshot is re-pulled.
The county map reads CDC’s county file, 2023 and every year back to 2001 (read 10 October 2026) — the same file the tick-bite steps read — and is refused unless the file hashes to the one read that day and its counties add up to no more than CDC’s national total for each year. A county’s rate is LymeHQ’s arithmetic on that count and the Census Bureau’s population for the same year (read 16 October 2026). Every source is listed under the county map with the day it was read.
Data retrieved from data.cdc.gov on 2026-08-27
Related guides:Case counts & trendsTick preventionEducation library