Founded in 1966; early participants or possibly co-founders include Marion Zimmer Bradley, her sister-in-law Diana Paxson, Poul Anderson, and others from the Little Men sf fan group. Walter Breen was involved with the group on the West Coast.
A suit against the SCA in 2007 followed a criminal conviction of a chapter in Pennsylvania; this suit mentioned the early history of the SCA, Breen, and MZB.
http://yusefsjournal2.blogspot.com/2012/01/sca-fail.html
Details of the civil suit settlement and aftermath here: http://file770.com/?p=9800