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Illinois: Risks & Trends

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Same standard as every other page on this site: every figure below is independently sourced, and figures that vary across sources, or measure genuinely different things, are flagged as such rather than collapsed into one number that looks more precise than the underlying data actually supports.

The Tri-State Tornado (1925): the deadliest tornado in U.S. history

MetricFigure
Illinois deaths 588 of 695 total across IL/IN/MO
Murphysboro, IL deaths alone 100+
Total three-state injuries 2,027
Total path length 219 mi
Forward speed through Murphysboro 62 mph
Peak rating F5
Total duration 3 hr 45 min

Illinois absorbed the overwhelming majority of this storm’s death toll, and its combination of an unusually long, unusually fast-moving path is part of why: at 62 mph forward speed, there was far less warning time than a typical tornado allows, even by 1925 standards before modern radar existed.

The November 17, 2013 outbreak: the same risk, modern data

MetricFigure
Total tornadoes statewide, single day 77
Illinois deaths 8
Injuries 190+
Damage ~$1.6 billion
Strongest tornadoes Two rated EF4, together responsible for 5 of the 8 deaths

Why this is the relevant modern comparison, not just a historical footnote

Nearly 90 years separate these two events, but they demonstrate the same underlying risk: Illinois can produce large, multi-tornado outbreaks in a single day. The 2013 outbreak is the deadliest and costliest November tornado event in Illinois history specifically, showing this risk isn’t confined to the traditional spring tornado season either.

The New Madrid Seismic Zone: a standing probabilistic risk

MetricFigure
50-year chance of a repeat of the 1811-12 earthquake sequence 7-10%
50-year chance of a magnitude 6+ earthquake in the zone 25-40%
100-year chance of a damaging earthquake in Cairo, IL 50-75%
Risk level for Springfield, Champaign, and the Chicago area 5-25%

Unlike the tornado risk above, this is a standing, probabilistic condition rather than a single documented event, the same kind of framing this site uses for California’s UCERF3 figures and Oregon’s Cascadia probability. Southern Illinois carries meaningfully more of this risk than the rest of the state.

The January 2019 polar vortex: a record that still stands

MetricFigure
Coldest temperature ever recorded in Illinois (Mt. Carroll) -38°F
Chicago deaths 3
Midwest-wide deaths 21+
Illinois hospital treatments for cold injury, single 3-day window 144

What these have in common

Illinois carries three structurally different hazard mechanisms, wind, seismic, and extreme cold, none of them hypothetical: the state holds the record for the deadliest tornado in American history, sits within meaningful reach of a major fault system, and set its own all-time cold record within the last decade. A household’s specific exposure depends heavily on where in the state they are, southern counties carry more earthquake risk, the whole state carries real tornado risk, and extreme cold is a statewide concern every winter.

Sources