Death by heat was a fairly common occurrence for a sizeable number of Americans during the 20th Century, particularly in the first half of the century. Between 1900 and 2000 there were 65,838 heat related deaths in the United States. These data were gleaned from the, Mortality Statistics from the US Census, Vital Statistics of the US (Part II, Mortality) and Storm Data. This is a conservative, hard count of heat-related deaths. However, it is possible that there is an under count of heat deaths in the early 20th Century, because not all states reported mortality data in the 1900-1920 era. This is particularly true of the 1901 heat wave in which over 4012 heat fatalities occurred in the Northeast and Midwest. Some investigators have speculated that the true mortality of that heat wave might have been over 9000 deaths.

During the century there were fourteen heat waves that resulted in more than 1000 deaths in each episode. Exceptionally high numbers of heat fatalities occurred in the early part of the century; four heat waves - 1901, 1911, 1934 and 1936, accounted for 15,113 deaths. Heat-related fatalities decline after WWII - as air conditioning becomes more affordable, nonetheless, there were three heat waves since 1950 that posted more than 1000 deaths in each year (1952, 1980 and 1995).

Geographically, the lion's share of the century's heat mortality is focused in the urban areas of the Northeastern and Upper Midwestern regions. At various times during the century, New York City, Philadelphia, Boston, St. Louis, Chicago and Pittsburgh all have had heat wave episodes of more than 500 deaths per city.

Although heat-related deaths declined in the latter part of the century, the implication for the future is still ominous. Cities in the above mentioned regions are extremely dependent on electrical power for air conditioning needs. Any future disruption of this power supply during a heat have of three days or more, could yield large numbers of heat-related deaths.