Several links which talk about the origins of Swing Dancing:

http://www.savoystyle.com/history.html

http://www.streetswing.com/histmain/z3wcs1.htm

http://www.centralhome.com/ballroomcountry/swing.htm

http://people.cornell.edu/pages/kpl5/f_Link5_overview.html

Interesting discussion on the origins of Swing dancing from DanceTalk message board.