All kinds of people read mystery and crime fiction. Trying to place mystery readers in a nice well defined niche must drive marketing professionals to distraction. Mystery fans are everywhere--they have trampled the usual categories of age, culture, gender, and economic status into oblivion. Here are some discussions of the reasons this genre of fiction is so popular.
Cohen, Michael. Murder Most Fair: The Appeal of Mystery Fiction. PR830 D4 C6 2000
These Internet sites provide information on organiztions for writers and fans as well as fan gatherings and conventions.
Bouchercon. Bouchercon is the largest annual mystery/crime convention and is home to the Anthony Awards.
Crime Writers of Canada. Links to member bios, author events, and more.
International Thriller Writers. Includes information on ThrillerFest activities.
Malice Domestic. This popular annual convention is dedicated to traditional and cozy mysteries and is the home of the Agatha Award.
Mystery Readers International. The world's largest organizations of mystery readers and fans. The web site has lots of current information.
Mystery Writers of America. Information on authors (and their books) who are members of the MWA, regional associations, and Edgar Awards winners and nominees. A good place to look for speakers.
Sisters in Crime. An association of women writers and female characters in mysteries. In addition to providing information on its members, the site has a list of mystery bookstores.