The county most often under a severe thunderstorm (≥1" hail and/or ≥60 mph winds) Marion County, Kansas. Note the interesting "island" of high frequency of severe thunderstorm watches around Washington, DC. Its frequency of severe thunderstorm watches is higher than parts of Kansas and Oklahoma. I wonder if that is partly political -- the desire not to "miss one" a storm forecast for the nation's capital?
To a meteorologist, there is nothing surprising about tornado watches. To the general public, it might be surprising that the Deep South, especially in recent decades, has had the highest frequency of tornadoes. The county most often under a tornado watch are Lincoln and Lawrence counties of Mississippi.