Photo: Unknown author Unknown author · Public domainFlood mapping exists for Cornwall: 8 on record, latest by Raisin Region Conservation Authority
Wildfire barely registers for Cornwall, at 0% of the land within 25 km since 1986 (0.000% a year). Earthquakes add more: NRCan’s model puts building losses at $0.20 a year per $1,000 of value, against $0.030 for the typical town. About as many homes carry radon around Cornwall as elsewhere, 6.1% over the guideline where the typical town has 6.6%. Hazard risk gives Cornwall a grade of C, from earthquakes and radon alone.
What stands out about Cornwall’s hazards
Four national sources, each read for Cornwall: earthquakes, radon, past fires and flood studies.
What Cornwall faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Wildfire
Earthquakes
Radon
Flood study
Hazard risk in Cornwall: C
Seismic risk and radon set Cornwall’s grade, wildfire can drag it down, and flood mapping stays out of it.
Its place: #829 of 866 in Ontario and #2,063 of 2,589 Canadian towns.
How sure: The seismic figure is a long-run average from NRCan’s model, not a prediction. Small fires and grass fires are largely missing from the national burned-area record.
Few fires near Cornwall: 0% within 5 km, 0% within 25 km
Past fire around Cornwall’s homes, from the national burned-area record, with the fuel within 5 km.
Around Cornwall fire takes 0.000% of the land in a typical year, the typical Canadian town 0.000%, which is low.
Close to Cornwall there is little to burn (2.4% forest fuel within 5 km), but 7.2% of the land within 25 km is forest.
Shares of land within 5 and 25 km of populated blocks: burned at least once in 1986–2025 (CWFIS burned-area composite), forest fuel and grass (fire behaviour fuel types, 2026, 250 m grid).
Burn rate a year, towns in Ontario · highest of 871
Among the 871 towns in Ontario, Sioux Lookout burns fastest (0.16% a year); Cornwall is with the 638 near zero.
Each bar: the yearly average share of land within 25 km of a town’s homes that burned, 1986–2025 (CWFIS); the seven highest towns of 2,500 people or more.
The low band holds 92% of Canada’s 2,610 towns, and Cornwall sits at its very bottom; only 7.5% are above it.
Bands of the yearly burn rate: low under 0.05%, moderate under 0.25%, high under 1%, very high 1% or more; towns of 2,500 people or more.
Fire danger and active fires (CWFIS)
Canadian Wildland Fire Information System: National Burned Area Composite 1986–2025 and fire behaviour fuel types (2026), Natural Resources Canada. Measured within 25 km and 5 km of each populated dissemination area; past fire, not a forecast.
Cornwall is on the flood map inventory: 8 studies, latest by Raisin Region Conservation Authority
What Canada’s Flood Map Inventory lists for Cornwall: who studied flooding and where to see their maps.
For Cornwall the inventory points to 8 studies, most recently Raisin Region Conservation Authority’s in 2024.
| Study | By | Year | Status |
|---|---|---|---|
| Eastman Drain 2024 | Raisin Region Conservation Authority | 2024 | final |
| Raisin River and St. Lawrence River Floodplain Mapping Update | Raisin Region Conservation Authority | 2020 | final · not public |
| South Branch Raisin River Storm Water Management Study | Raisin Region Conservation Authority | 2002 | final · not public |
| St. Lawrence River Floodline Re-Mapping Study | Raisin Region Conservation Authority | 1994 | final · not public |
| Gray's Creek Flood Plain Mapping Study | Raisin Region Conservation Authority | 1988 | final · not public |
| Hydrologic and Hydraulic Analyses Boales Drain | Raisin Region Conservation Authority | 1985 | final · not public |
| South Branch - Raisin River Flood and Fill Line Mapping | Raisin Region Conservation Authority | 1984 | final · not public |
| Water Management Study of South Raisin River | Raisin Region Conservation Authority | 1980 | final · not public |
Towns with a flood study on file
Flood maps are common in Ontario: 69% of towns have one, against 58% nationally, and Cornwall is among them.
NRCan Canada Flood Map Inventory: a study footprint touching the town’s boundary; towns of 2,500 people or more.
Mapping around Cornwall began in the 1980s; the 1980s saw the most work (4 of 8 studies), the latest in the 2020s.
Study dates as the NRCan inventory lists them, one count per study touching Cornwall.
The grade leaves flood out, since a study area says nothing about how many of Cornwall’s homes are at risk.
The inventory’s own caution (NRCan): “The Canada Flood Map (CFM) does not include every flood hazard map in Canada and may be incomplete or contain inaccuracies. It should not be relied upon as the official source of flood mapping information. Furthermore, if a map appears to be missing, this does not necessarily mean that the area has never been mapped. For the official version of a map, updated information, or confirmation of applicable regulations, please contact the local authority responsible for flood mapping.”
Natural Resources Canada, Canada Flood Map Inventory; links go to each study’s owner.
Earthquakes cost buildings in Cornwall $0.20 per $1,000 a year
Expected yearly building losses from earthquakes, from Natural Resources Canada’s model.
Cornwall’s $0.20 is about 6.6 times the typical town’s $0.030: it sits in one of Canada’s more active seismic zones.
Shaking damage a year per $1,000 of building value
At $0.20, Cornwall is above the typical town in Ontario ($0.043); Alexandria has the most at $0.21.
NRCan seismic risk model (2022): mean yearly building loss per $1,000 of value; medians of towns of 2,500 people or more.
12% of Canada’s 2,611 towns expect more shaking damage than Cornwall, which places it in the upper third.
Each column: the share of Canada’s towns of 2,500 people or more in that range of yearly loss per $1,000 (NRCan, 2022).
The loss is to Cornwall’s buildings alone, from ground shaking; infrastructure and secondary hazards are left out.
Natural Resources Canada, Canada’s Seismic Risk Model (2022), by census subdivision (2016 boundaries; a few 2021 subdivisions take their residents’ mean).
Some radon around Cornwall: 6.1% of area homes over the guideline
Long-term radon tests in homes across the survey area, against Health Canada’s guideline.
6.1% of tested homes around Cornwall were over the guideline, much like the typical Canadian town at 6.6%. For radon tests, the only official count covers all of the The Eastern Ontario Health Unit, Cornwall included.
Tested homes over 200 Bq/m³
Over 600 Bq/m³
Cornwall’s area, at 6.1%, is above the median in Ontario (4%), and 1% of its tests passed 600 Bq/m³.
Health Canada radon survey (2009–2011), by 2007 health region; medians of towns of 2,500 people or more.
Between 5% and 10% of tests over the guideline: Cornwall, and 37% of Canada’s 2,611 towns; 26% are higher.
Each bar: the share of Canada’s towns of 2,500 people or more whose survey area had that share of tests over 200 Bq/m³.
Basements, soil and how a house is sealed decide its radon, so in Cornwall only a test can say.
Health Canada, Cross-Canada Survey of Radon Concentrations in Homes (2009–2011).
Weather and fire alerts for Cornwall
Environment and Climate Change Canada issues the weather alerts for Cornwall; Alert Ready carries the urgent ones to phones, radio and TV.
| Alert | What it means |
|---|---|
| Warning | Severe weather is happening or about to: act now. |
| Watch | Conditions favour severe weather: be ready. |
| Advisory | Weather that is less severe but could disrupt the day. |
| Special weather statement | Unusual weather worth knowing about. |
| Special air quality statement | Poor air, often wildfire smoke. |
For fires near Cornwall, the national fire information system maps danger and active fires daily; local authorities give any evacuation order.
Weather alerts (ECCC) · Alert Ready · Fire danger and active fires (CWFIS)
Hazards in the places around Cornwall
Wildfire band, earthquake risk, radon and flood studies for each place nearby.
| Town | Wildfire | Quake $/1,000 | Radon | Flood study |
|---|---|---|---|---|
| Cornwall | Low | $0.20 | 6.1% | Yes |
| Akwesasne (Part) 59 1,947 · 2.6 km | Low | $0.14 | 6.1% | Yes |
| Akwesasne 2,562 · 14 km | Low | $0.22 | 8.2% | None listed |
| South Glengarry 14,355 · 15 km | Low | $0.20 | 6.1% | Yes |
| Long Sault 14,602 · 16 km | Low | $0.20 | 6.1% | Yes |
None of the places around has more fire nearby than Cornwall (low); Akwesasne (Part) 59 comes closest (low).
Radon is the survey area’s figure, so neighbours in one area share it.
Get ready for what Cornwall faces
Practical steps for Cornwall’s hazards, most pressing first.
- Test for three months in winter.
- Over 200 Bq/m³: fix it.
- Kits are cheap; pros test too.
- Never drive through floodwater.
- Move papers and medicines upstairs.
- Ask whether your street is mapped.
- Drop, cover and hold on.
- Strap the water heater down.
- Keep 72 hours of supplies.
- Has it had a radon test?
- Check the address on the flood map.
- Are flood and wildfire insured?
- Is earthquake cover included?
What this data can and can’t tell you
- Earthquakes are modelled. Shaking damage is modelled from the ground, the buildings and the odds of each quake, and published for whole subdivisions such as Cornwall’s.
- Radon is a survey. Radon figures pool the survey’s home tests by area: postal areas once their boundaries arrive, the 2007 health region around Cornwall until then.
- Wildfire counts one way. The wildfire figure is the share of land within 25 km of Cornwall’s homes burned each year from 1986 to 2025, past fire rather than a forecast, and it can only lower Risk.
- Flood studies aren’t flood zones. Flood studies cover areas of every size, which is why the page lists them for Cornwall without grading them.
Questions about flooding and hazards in Cornwall
How is Cornwall’s Hazard risk Grade worked out?
Hazard risk gives Cornwall C, weighing earthquakes and radon and counting wildfire only against it.
Is radon a problem in Cornwall?
6.1% of the 99 homes Health Canada tested around Cornwall topped the guideline; your own house needs its own test.
Does Cornwall flood?
A flood study covers Cornwall on Canada’s Flood Map Inventory; open the owner’s map to check a street, since flood isn’t graded.
Is Cornwall at risk of wildfire?
Very little by the national record: Cornwall’s band is low, with 0% of the land within 25 km burned since 1986, so wildfire doesn’t change its grade.
How big is the earthquake risk in Cornwall?
In NRCan’s seismic model, Cornwall’s buildings lose $0.20 per $1,000 of value in an average year.
Seismic risk: Natural Resources Canada. Radon: Health Canada. Wildfire: Canadian Wildland Fire Information System. Flood studies: Natural Resources Canada, Canada Flood Map Inventory. Contains information licensed under the Open Government Licence – Canada.
Sources: NRCan, Canada’s Seismic Risk Model 2022 · Health Canada, Cross-Canada Survey of Radon Concentrations in Homes · CWFIS, National Burned Area Composite and FBP fuel types · NRCan, Canada Flood Map Inventory. Under the Statistics Canada Open Licence.
Adapted from Statistics Canada (Census of Population 2021, population estimates 2025, 2021 census boundaries) under the Statistics Canada Open Licence; this does not constitute an endorsement by Statistics Canada. Neighbourhood names in some cities © OpenStreetMap contributors (ODbL).