Williamson County, IL

Supports FEMA checklist item B1-a Hazard identification

14 of the 18 National Risk Index hazards apply here.

Not applicable to this county per NRI, with no federal declaration and no Storm Events record since 1996: avalanche, coastal flooding, tsunami and volcanic activity. That is the evidence for leaving them out of the plan.

Highest expected annual loss (NRI, modeled): Earthquake, Inland Flooding and Strong Wind.

Not covered by NRI (local data needed): dam failure (incl. upstream dams); levee failure; flash flood as its own subtype; ice jams; debris flows; erosion (riverine and coastal); land subsidence and sinkholes; expansive soils.

The state hazard mitigation plan also lists hazards for this county; FEMA asks the plan to explain any hazard it leaves out.

Supports FEMA checklist item B1-b Hazard location

• Cold Wave, Drought, Hail, Heat Wave, Ice Storm, Lightning, Strong Wind and Winter Weather: Affects the whole county; national data give no location within it.
• Earthquake, Hurricane, Landslide, Tornado and Wildfire: Varies within the county: the census tracts with the highest National Risk Index rating for this hazard are listed. FEMA's Resilience Analysis and Planning Tool (RAPT) maps the National Risk Index for every tract (https://www.fema.gov/emergency-managers/practitioners/resilience-analysis-and-planning-tool).
• Inland Flooding: The FEMA Flood Insurance Rate Map (FIRM) is the required location source for flooding. See the FEMA Flood Map Service Center (https://msc.fema.gov) for this county.

Supports FEMA checklist item B1-c Hazard extent

Storm Events records for 12 of the 20 NOAA event-type groups mapped to the 18 hazards, with the scale, observed range and worst recorded event for each; the others say which local data are needed.

• Hail: 3 in hail, 2023-06-30; same size also recorded on 2017-02-28
• Thunderstorm Wind: 87 kt (100 mph) estimated gust, Thunderstorm Wind, 2012-02-29; same speed and measurement basis also recorded on 2000-01-03, 2009-05-08
• Tornado: F4 tornado, 1982-05-29, 17 mi path length (whole path, pre-1996), 400 yd wide, $250,000,000 property; crops not recorded (1982 dollars), 10 direct deaths, 181 direct injuries

Supports FEMA checklist item B1-d Previous occurrences

Federal declarations for this area: 9 declarations covering 6 separate hazard incidents counted in this packet; each with type, dates and county Public Assistance dollars.

New since the last plan (approved 2023-07-05): none.

2 statewide declarations listed separately.

Hazards with no Storm Events record and no federal declaration are stated as such (8 of 18).

Storm Events history: 754 records (notable ones in the PDF, all of them in the Excel file).

Supports FEMA checklist item B1-e Probability of future events

FEMA annualized frequency (modeled) for each hazard, with a descriptor from a scale defined in the packet.

• Highly likely: Hail, Lightning, Strong Wind and Winter Weather
• Likely: Cold Wave, Drought, Heat Wave, Ice Storm, Inland Flooding, Landslide and Tornado
• Possible: Hurricane

Historical frequency by intensity band (tornado, hail, wind): 9 bands from Storm Events.

Supports FEMA checklist item B1-f Hazards that vary across jurisdictions

Range of census tract risk scores within the area for 14 of the 18 hazards (18 tracts; rated tracts only).

16 jurisdictions: plan clock, repeat-flood count, Public Assistance dollars and event records naming the place (starting figures from federal data).

County Public Assistance in B1-d also includes applicants filed under the county that are not jurisdictions in this plan (for example state agencies, special districts and nonprofits), so the jurisdiction rows add up to less.

Supports FEMA checklist items B2-a and B2-b Vulnerability and potential impacts

The packet's table gives county-level starting figures; the plan describes impacts for each jurisdiction and its own assets.

Storm Events damage since 2023-07-05: $25,818,000 in county-coded records (44 records); $277,000 reported for the zone (55 zone records). Data through 2026-06-30; nominal dollars.

Local data needed

To gather:

• Critical facilities and lifelines per hazard
• A problem statement per jurisdiction per hazard
• Changes in development in hazard-prone areas since the last approval, or a statement of none (E1-a)
• Future assets

Supports FEMA checklist item B2-a Vulnerability (county context)

Population 67,101; building value $16,135,072,999 and agriculture value $44,705,944 (total, not at risk).

National Risk Index rating Relatively Moderate; social vulnerability Relatively Moderate; community resilience Relatively High.

Supports FEMA checklist item B2-c Repetitive loss properties

Repetitive-loss properties, FMA definition (44 CFR 77.2): 0 repetitive loss, 6 severe repetitive loss. NFIP insurance definition: 13 and 3.

Mitigated 3; insured 1; NFIP data as of 2026-08-02. Counts by occupancy group and for each jurisdiction are in the packet.