The Institute in Arizona has its own unique history. In 1949, IBVMs of the North American Branch settled in Phoenix, Arizona, to teach at St. Gregory School and eventually to serve in other schools and in the diocesan office.

In 1954, five Sisters of the IBVM Irish Branch emigrated from Ireland to teach at Saints Simon and Jude School in Phoenix. As more sisters came from Ireland and a few from Spain and England, they were able to undertake ministries in Prescott and Flagstaff.

Also in 1972, the Irish Sisters became a Region of the Irish Branch. While they were not a large enough group to be a Province, they had their own Regional Government and representation at General Congregational Meetings. By 1974, they celebrated the opening of a Novitiate and the reception of three young American women in to the community.

For almost 60 years, the sisters of the two different branches of the Institute have been friends and collaborators in spirit, prayer, and ministry, but separated by governmental structures.

In 2003, the Reunion of the Irish and North American Branches brought these two groups together simultaneously creating the Loreto/Loretto Branch and a United States Province. After careful consideration and prayer, the sisters of the Arizona Region (Irish Branch) joined the United States Province.