Chester County, Pennsylvania

What hazards hit Chester County most?

The most frequent records are severe thunderstorm wind events: 782 since 1957. 50% of its severe thunderstorm wind events since 1957 fell in June and July. The rank column places the county among Pennsylvania's counties by days with a record per 1,000 square miles of land over each hazard's complete period.

Source: NOAA NCEI Storm Events Database (county and forecast-zone records attributed to the county; a zone record shows its own totals on each county it covers). Days: dates with at least one record of the hazard in the county. Ranks: days with a record per 1,000 square miles of land (Census Bureau 2024 Gazetteer), since 1950 for tornadoes, 1955 for hail and thunderstorm wind, 1996 for the rest.

How many tornadoes has Chester County had?

NOAA records 29 tornadoes in Chester County from 1953 to 2023, the strongest rated F3, with 2 deaths and 32 injuries recorded in the county. That is 9th of 67 Pennsylvania counties by days with tornadoes per 1,000 square miles since 1950. A tornado that crossed a county line is counted in each county it touched, with the length of its path inside the county.

Counted as whole tornadoes rather than county records, the Storm Prediction Center's database holds 31 tornadoes whose track touched Chester County since 1950 (NOAA's county records number 29: they file a crossing tornado once per county segment, and the two databases differ on some tracks); along their whole tracks they killed 3 people, 2 of them in Chester County.

Map of the strongest tornado tracks in Pennsylvania.

Source: NOAA NCEI Storm Events Database, tornado records by county (path length in the county, maximum width); ratings as published: F scale before February 1, 2007, EF scale after. Whole-track figures: NOAA Storm Prediction Center tornado database (1950-2025). SPC severe weather database.

When was the last damaging storm in Chester County?

The most recent record with damage, injuries or deaths is the July 9, 2025 flash flood ($5,000 in damage in 2025 dollars).

Source: NOAA NCEI Storm Events Database; every record of 2025-2026 is listed, earlier ones when they caused deaths, injuries or $250,000 of damage (2025 dollars), and every tornado.

The deadliest and costliest records

A damage figure marked "step" is a record from before 1993: NOAA then filed damage by category, and the figure is the category as entered, in the dollars of that year, not an estimate of the loss.

Source: NOAA NCEI Storm Events Database: deaths and injuries direct and indirect; damage is property plus crops as estimated by the National Weather Service, converted to 2025 dollars.

Is it getting more frequent?

Records per decade for Chester County's most frequent hazards. Counts rose everywhere after 1996, when NOAA began recording every event type, so compare decades within a hazard's complete period only (the shaded cells come before it).

Source: NOAA NCEI Storm Events Database, records per calendar decade; zone records from the CZ_TYPE field (Z).

What time of year?

50% of its severe thunderstorm wind events since 1957 fell in June and July. The two busiest months are in violet.

Source: NOAA NCEI Storm Events Database, records by the month they began.

Federal disaster declarations for Chester County

FEMA's register lists 26 declarations that include Chester County: 18 major disasters, 8 emergencies and 0 fire management assistance declarations. Most were for hurricane (7) and flood (6).

Source: FEMA OpenFEMA Disaster Declarations Summaries (v2), declarations through October 2, 2026; one declaration is counted once however many areas it names. OpenFEMA dataset page.

How many floods has Chester County had?

NOAA's Storm Events Database holds 316 flood or flash flood records for Chester County from 1996 to 2025, on 177 days, with 3 deaths. By flood insurance claims since 1978 (OpenFEMA, as of September 8, 2026), Chester County ranks 199th of 2,942 U.S. counties.

The National Flood Insurance Program has paid $37.6 million on 1,914 claims filed in Chester County; the most in one year was 215 in 2021. Claims count insured losses only: uninsured flood damage is not in this file.

Source: FEMA OpenFEMA NFIP Redacted Claims, as of September 8, 2026; claims by year of loss, payments in the dollars of the year paid. OpenFEMA dataset page.

FEMA's modeled risk for Chester County

FEMA's National Risk Index rates Chester County Relatively Moderate overall, with an expected annual loss of $173 million. These are FEMA's model estimates of future loss from 18 hazards, not a count of what happened; they can differ from the record above.

Source: FEMA National Risk Index, county table, December 2025 release. FEMA's National Risk Index map.

Counties that share a border with Chester County

1. Chester County 2,132
2. Berks County 2,021
3. Montgomery County 1,973
4. New Castle County, DE 1,569
5. Delaware County 1,367
6. Lancaster County 1,177
7. Cecil County, MD 1,043

Source: U.S. Census Bureau county adjacency file; NOAA NCEI Storm Events Database, records since 1950. The Census Bureau's adjacency file.

Next

• Tornadoes in PennsylvaniaEvery Pennsylvania tornado since 1950 and the counties with the most per square mile
• Severe thunderstorm wind in PennsylvaniaThe state's severe thunderstorm wind events, by county, year and month
• The Pennsylvania recordEvery hazard in the state, its deadliest events and its federal declarations
• FEMA's risk rating for each hazard in Chester CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Chester County's FEMA declarations (CSV)26 rows: every declaration that named the county, for your own analysis