Why is the Streamwood, Illinois area so murdery, by episodes?

The Streamwood area is the western and north-western reach of Chicago's commuter belt: nine suburbs spread from the centre out to twenty-four miles, half an hour to seventy minutes from the city, across Cook, DuPage and McHenry counties. Streamwood itself was Hanover Township farmland in 1950, about 800 people, and incorporated in 1957. The towns around it filled in the same way, farms turned into subdivisions thrown up for blue-collar families.

The cases run from 1966 to 2007, and every decade has at least one. Three episodes touch 1980 or the two years either side of it. Episode 184, at the centre, holds eight victims across six cases between 1987 and 1997. Episode 257, out at twenty-four miles, holds four from a single day in 1988. Between them that's twelve of the twenty-nine. Of the other seven episodes, five hold three victims each and two hold one, spread across as many towns.

Nine towns on Chicago's outer edge, one episode apiece and between one and eight victims each, add up to third place overall.