(I posted this to the "History of Sororities" thread several days ago. It is relevant here.)
To add to this is the P.E.O. Sisterhood, founded in 1869 at Iowa Wesleyan College.
Of its seven founders, some had been asked to join the I.C. Sorosis at IWC but some had not. They wanted to stay together so they founded "a society of [their] own." P.E.O. chose to retain English letters and to become a community, rather than a collegiate, organization in the early 1900's. Chapter Original A at IWC is Alpha Xi Delta; the I.C. chapter (Pi Phi for lo these many years--Iowa Alpha?) is still there.
P.E.O. is larger than any one NPC group in terms of initiated members and chapters. Probably also larger in terms of assets in the charitable foundation which funds P.E.O.'s projects. Many, many NPC members are also P.E.O.s. (
www.peointernational.org will tell you more.)
AGDAlum (who is also a P.E.O.)