This was a 3.8 magnitude quake, quite small (the one in Haiti a month ago, 7.0, was 1600 times stronger!).

Here is a map showing the earthquakes that have hit Northern Illinois in the 20th Century:

20th Century Earthquakes - Northern Illinois

This works out to about one every six years, with none over 4.0.  Here is the exact location of the tremor, which was 10 km below the surface:

Epicenter, Lily Lake Earthquake, Illinois February 2010

And here is a map of where the quake was felt, although there were reports as far away as northeastern Arkansas, southeastern Minnesota and western Ohio:

Shake Map, USGS, Lily Lake Earthquake, Illinois Feb. 2010

This map makes the area look quite mountainous!  It’s really basically flat, I’m afraid.  I will add to this post in the near future…..