There seem to be some contradictory claims being put forward. Here
are the organizations I have identified, with claims as made by or for
them cited directly from the relevant web sites.
The National Organization for Women (NOW) is the largest organization
of feminist activists in the United States. NOW has 500,000
contributing members and 550 chapters in all 50 states and the
District of Columbia.
Concerned Women for America: There is a claim that CWA is larger than
NOW: Beverly LaHaye and a handful of women founded Concerned Women
for America. Soon they became the largest women's organization in the
country, more than double the size of NOW in actual dues-paying
This site claims CWA has over 500,000 members
However, the CWA web site seems to be coy about stating membership
figures. I could only find a figure of 17,784 subscribers to their
mailing list. Also, their membership structure seems to be rather
loose: Giving a donation of any dollar amount makes you a member of
CWA. We welcome all like-minded women and men.
Hadassah: the largest women's and the largest Zionist membership
organization in the United States, with more than 300,000 members.
Chi Omega Sorority: With over 240,000 initiated members and 170
collegiate chapters, Chi Omega is the largest sorority and second
largest women's organization in the United States
Daughters of the American Revolution has over 170,000 members
The American Business Women's Association (ABWA), founded by Hilary
A. Bufton in Kansas City, Missouri, has been helping working women
meet their personal and professional goals for over 50 years. At over
70,000 members, ABWA is the fourth largest women's organization in the
Search strategy: largest womens organization second largest
womens organization third largest womens organization
I hope this has answered your question, but please request further
clarification if required.