The fraternal order Alpha Phi Omega which is historically linked to Boy Scouts, removed the restriction of sex for membership back in 1976 around the same time that MOST Scouting organizations worldwide did the same.
Old frats were grandfathered in to remain single sex but about 10 years ago, the transition was completed..
One splinter fraternity broke off upon the completion of the transition, over the politics.
Alpha Phi Omega is huge:
“350 campuses, an active membership of over 25,000 students, and over 400,000 alumni members. There are also 250 chapters in the Philippines, one in Australia and one in Canada. “
The boys-only splinter fraternity formed in 2008 has 6 chapters.
Sigma Xi – University of Maine (Est. May 15, 1967)
Zeta Theta – Drexel University (Est. May 16, 1948)
Pi Chi – Duquesne University (Est. May 15, 1966)
Psi Delta – University of Maine at Machias (Est. May 14, 1972)
Nu Mu – University of Minnesota at Duluth (Est. May 25, 1961)
Alpha Gamma – Alcorn State University (Active)
The change also began in the 1970s with the Boy Scouts of America moving over to Scouting/USA by 1977, but resistance was noisy and by 1980, conservative elements took over and remained in charge for about 35 years, but retaining co-ed in older teen and adult level programs as well as many of the other expansions of the 1970s.
England also switched to co-ed in 1976 and in 2011 there were more girls than boys enrolling.