Roman Catholicism

The Roman Catholic Church has existed in New Orleans since the mouth of the Mississippi River was discovered by Jean-Baptiste Le Moyne de Bienville in 1718, just over three hundred years ago. In 1727, Ursuline nuns arrived from France to minister at the hospital and to teach young girls. The Ursuline Nuns came from Canada which at the time was the home of the Biship of Quebec the governing Catholic body for the Americas at the time.

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The Ursuline Nuns wielded considerable influence in the early development of New Orleans. When they first arrived, there was no convent for them. They were allowed to reside in the Governor's own residences until eventually  the King of France was convinced to fund the construction of a convent  for them in 1734. In 1752, the convent was rebuilt in the place where it stands today. In 1788 a great fire know as the "Good Friday Fire" because it occurred on Good Friday, burned most of the buildings in New Orleans Leaving the Ursuline Convent in tact. Many believed that the Convent was spared by God because they prayed and placed a small "Sweetheart Statue" of the Virgin Mary in one of the Convent's windows. This statue is on display to this day in the Ursuline Convent Museum. 

          

Ursuline Convent Museum

“The history of the Catholic Church and the history of the city of New Orleans cannot be separated. They are very much intertwined and have been for 300 years”

- Archbishop Gregory M. Aymond, January, 2018

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In 1718, when Jean-Baptiste Le Moyne de Bienville established New Orleans on behalf of France, he was accompanied by a priest of the Roman Catholic Church. The Priest planted a catholic cross and painted the  fleur-de-lis on a building erected at the site.
During this time, Roman Catholicism was the only legal religion to practice. According to Catholic Doctrine, every member of every household had to be baptized Catholic. This included slaves and servants. This remained the status quo even after the Spanish took control over New Orleans in 1763, because Spain was also a Catholic nation. Since then, there were strong French and Spanish influences supporting the Catholic Religion until the United States' acquisition through the Louisiana purchase in 1803.
To this day, the majority of New Orleneans identify as Roman Catholics. New Orleans also boasts the largest population of African American Catholics in the United States.

References:

Harpaz, Beth J. “Catholic Church Plays Central Role as New Orleans Marks Tricentennial.” Crux, Associated Press, 5 Feb. 2018, cruxnow.com/church-in-the-usa/2018/02/05/catholic-church-plays-central-role-new-orleans-marks-tricentennial/.