Ticks in Ontario:
2026 Statistics, Species & Risk Data

In Ontario’s established (endemic) blacklegged tick risk areas, approximately 20% of blacklegged ticks carry the Lyme disease bacterium Borrelia burgdorferi — and the rate exceeds 20% in Toronto and Northwestern Ontario, according to the Northwestern Health Unit’s 2023 drag sampling and City of Toronto Public Health. Province-wide infection prevalence rose from 8.4% in 2008 to 19.1% in 2012 (Public Health Ontario passive surveillance). The 20% threshold is also the clinical cutoff used to determine eligibility for post-exposure prophylaxis. Outside established risk areas, infection prevalence is near zero — so the figure should always be framed as applying to risk areas, not the whole province.

Only one tick species in Ontario transmits Lyme disease: the blacklegged tick (Ixodes scapularis), sometimes called the deer tick. It accounts for roughly 55% of ticks submitted to Public Health Ontario’s passive surveillance program and also carries anaplasmosis, babesiosis and Powassan virus. The American dog tick (Dermacentor variabilis), Ontario’s second most commonly submitted tick at about 36% of submissions, does NOT carry Lyme disease, though it can rarely transmit tularemia and Rocky Mountain spotted fever.

43 tick species have been recorded in Ontario, according to Public Health Ontario’s The Ticks of Ontario Synthesis (2nd Edition). Of those, 12 are established, 17 are adventive (carried in by migratory birds and wildlife) and 14 are travel-related. Only the blacklegged tick transmits Lyme disease, and the blacklegged tick and American dog tick are the two species you are most likely to actually encounter.

Blacklegged ticks can be active any day the temperature rises above 4°C, including mild winter spells, according to Public Health Ontario. The peak human-biting season is May through July, when tiny poppy-seed-sized nymphs emerge and cause most Lyme disease transmission. A second peak occurs in September and October when adult blacklegged ticks are most active. In practice, Ontario residents should check for ticks after any outdoor activity from early spring through late fall.

Yes. Blacklegged tick established risk areas have expanded steadily since 2015 — from isolated Great Lakes shoreline pockets to most of southern Ontario plus pockets in the northwest, according to Public Health Ontario’s Vector-Borne Disease Tool. In 2025 alone, 13 new risk areas were added across 6 of Ontario’s 34 public health units. Human Lyme cases reflect the same trend: Ontario reported 2,369 cases in 2024, up 27% over 2023, and the most of any province (PHAC).

The highest blacklegged tick infection rates are reported in Toronto and Northwestern Ontario, where more than 20% of ticks test positive for the Lyme bacterium (Northwestern Health Unit, City of Toronto). Established risk areas now cover most of southern Ontario, with notable concentrations along the Great Lakes shorelines, the Oak Ridges Moraine, the Niagara Escarpment, and eastern Ontario. For a detailed neighbourhood-level breakdown of the worst tick areas, see our guide on whether ticks are dangerous in Ontario.

Blacklegged ticks generally need to be attached for 24–36 hours before they can transmit the Lyme bacterium Borrelia burgdorferi, which is why daily tick checks after outdoor activity dramatically reduce risk. If a blacklegged tick is found attached for 24 or more hours in an established risk area where infection prevalence exceeds 20%, a doctor may prescribe a single preventive dose of doxycycline within 72 hours (post-exposure prophylaxis). This page is educational and not a substitute for medical advice — contact your doctor, Telehealth Ontario, or your local public health unit after a tick bite.

No. This page aggregates publicly available tick and Lyme disease statistics from Public Health Ontario, the Public Health Agency of Canada, and other official sources for educational purposes. It is not diagnostic. If you have a tick bite, a bullseye rash, or unexplained symptoms after possible tick exposure, contact your family doctor, Telehealth Ontario (1-866-797-0000), or your local public health unit. In an emergency (facial drooping, irregular heartbeat, or severe headache with neck stiffness), go to an Emergency Room.